
Given a drawing pen, I decided that the best thing to do was to immediately not use it with drawing paper. SORRY COPIC.
Another little treat courtesy of JetPens :) I may just review all of them in a row (yes, there are others; it was like being adopted by Santa Claus in the middle of May or something—a.k.a. the best thing ever). Another round of thanks to Brad and JetPens!
Now, to business.

BUSINESS.
I’d thrown the Copic drawing pen on my wishlist on whims and whimsy, on knowledge that Copic was a solid brand whose products, though a little pricey, were a good investment (many Copic products have replacement nibs, replacement cartridges, etc. for their pens/markers/whatevers), and on the claim of “waterproof” in the title. I will go ahead and reveal that some of my consternation with this pen would have been avoided had I carefully read the description below the picture on the JetPens website. We’ll get to that in time. Let’s open up the pen.

It's a fountain pen oh my whaaaat?!
This isn’t even hinted at in the pen’s JetPens title, but the Copic drawing pen is a disposable fountain pen. What’s that you say? DISPOSABLE FOUNTAIN PEN, WHY ISN’T THAT JUST LIKE THE—yes, it is just like the Sailor Ink Bar disposable fountain pen. So much so that I cannot review the Copic Drawing pen without repeatedly drawing comparisons between the two.
The body of the Copic drawing pen sports the biggest differences between the two. It is both thicker and longer than the Sailor Ink bar, with cap on and with cap off. There’s slightly more room between the clip and the cap on the Copic. The Copic, though being lightweight due to its almost-entirely-plastic construction, is slightly (I mean so slight that you might think you’re just hallucinating it) heavier than the Sailor Ink Bar; given that the Copic is slightly bigger, no one should be surprised by this.
The plastic body of the Copic feels as though it’s constructed of about the same material as the Ink Bar, but the Copic body is a metallic-colored, subtly sparkly silver with black accents on the cap, clip, and end of the pen. There’s also much more information printed on the body of the Copic; the back side (not pictured) has printed on the barrel itself a barcode, and some advice written in both Japanese and English (“DO NOT SHAKE HARD AND DROP. INK MAY LEAK” and “REPLACE CAP WHEN NOT IN USE.”).
Careful application of the teeth reveals that, like the Ink Bar, the Copic drawing pen’s end piece (the end that’s not the cap) can be removed, opening the potential to nullify the “disposable” death sentence.
The design of the pen is otherwise of little note; it’s a simple, low end (or, intended to be relatively low end, since it’s supposed to be disposable) art supply. The design is unobtrusive, not really intended as the focus of the pen.

This is the focus of the pen. The part that writes. Copic drawing pen, in focus, between two Sailor Ink Bars.
The Behance Dot Grid paper was not the best medium for getting a feel for this pen. On the Behance paper, writing with the Copic drawing pen was a bit laborious—lots of resistance as I pushed the pen across the page, forcing me to grip the pen more tightly, which quickly became an uncomfortable situation. The Ink Bar also doesn’t perform as smoothly on the Behance paper, but it’s still smoother than the Copic drawing pen. It almost felt like there was some minuscule aberration on the nib of the Copic drawing pen that would ever so slightly catch on the page as I wrote, just enough to make more effort necessary in writing.

They're like BROTHERS. Clone brothers.
But in drawing, this wasn’t as much of a problem. I did have some issues with the Copic drawing pen not wanting to put down the amount of ink it was supposed to on the page, especially if I paused to contemplate a line or mark, but sometimes it would be finicky right out of the cap. In general, however, drawing and doodling went pleasantly. I don’t know what it is about the marks I make when drawing, but I always have more luck with achieving smoothness in the drawings even when the pen is being a bear to write with.
Trying the Copic drawing pen on different papers yielded much better results. Not the slickest stick I’ve put to a piece of Clairefontaine paper by any stretch of the imagination, but certainly no longer having the problem of writing resistance. Typical standard acceptable writing for a fountain pen on Clairefontaine paper. At that point, the writing experience was much closer to that of the Ink Bar; I daresay the two were almost indistinguishable.

What's there to distinguish when you have THE SAME NIB?
The Copic also took well to my Strathmore drawing paper, which I think allows it to retain with flying monocolor its title of “drawing pen.” The other bit though, the “with Waterproof Ink”…not only is that not true, but the description on JetPens itself explicitly states “Though permanent, the ink is water resistant but not waterproof and so will bleed slightly if brushed over with water.” Dear JetPens: please change the listed title of this pen to reflect WHAT YOU ALREADY KNOW TO BE REALITY. The congruency would make me happy. Much love.

Look at the Ink Bar on the left and the Copic. They both have the number 2 on the left bottom of the black plastic under the nib. You see it? I WILL NOT LET THIS POINT GO, YOU GUYS. I HAVE TOO MANY PICTURES FOR THAT.
But the body of the pen itself never claims to be waterproof. “COPIC PROOF,” it says. Lucky for us, I have some Copic sketch markers. I’ve tested this twice now, with a Cadmium Red Copic sketch marker, a Cool Gray No. 5 Copic sketch marker, and a Prismacolor True Blue marker. I wrote with the Copic drawing pen, then wrote with the Ink Bar, both on Strathmore watercolor paper, and then, from right to left, marked the marker over first the Copic drawing pen sample, then the Ink Bar sample. I’ll have to scan this for you guys tomorrow when I have scanner access, because I could barely believe it myself:
The Sailor Ink Bar is more Copic-Proof than the Copic Drawing pen.
No smudging with either marker on the Ink Bar writing samples. Smudging with both markers on the Copic drawing pen samples. I’m sort of flabbergasted. Let’s cut to another picture.

LOOK A SHINY DISTRACTION
Here are the facts. The Copic drawing pen costs more than the Sailor Ink Bar. The Copic drawing pen claims to be capable of doing more than the Sailor Ink Bar, even though my tests show that this is not true. They are both allegedly disposable fountain pens. They both have the same nib. The Copic drawing pen has darker ink, but that ink also smears slightly on the one task it is explicitly designed to not smear on.
The only thing the Copic really has over the Sailor Ink Bar is that the Copic drawing pen has not been discontinued by its manufacturer (WHY SAILOR WHY?). They are both good, cheap, “disposable” fountain pens that are good for drawing. But you’d be better off, while supplies of the Ink Bar last, buying two Sailor Ink Bars instead of one Copic drawing pen.
Now, I admit I’ve tried far more Sailor Ink Bars (about half a dozen now) than Copic drawing pens (one, so far). It’s possible that, on average, these two pens perform about the same, and I just got a Copic drawing pen that is slightly below the average. The difference in ink performance, however, is not as easy to write off.

I bet if I'd photoshopped the Copic Drawing pen to have a white body, you would think these were all Sailor Ink Bars. For now, you will just have to use your imagination.
Copic Drawing Pen with Waterproof Ink – 0.2 mm – Black at JetPens
and, for the sake of your convenience:
Sailor Ink Bar Disposable Fountain Pen – Fine Nib – Black at JetPens
EDIT: As promised, here’s the Copic drawing pen vs. Sailor Ink Bar test with Copic and Prismacolor markers

Markers were pulled from right to left. Very clear in the close-up which one is better.