Yes and no. They are compatible, but Steve has done a LOT of work getting his cartomizers to be top notch. Take that for what it's worth as I'm working with him right now, but his are the best I've had, especially the newest ones.
Not all cartomizers are created equal. In fact, not all cartomizers are created in the same factory. I've noticed that 901 tips (amputated to replace the little white thing) fit genuine VK cartomizers snugly, but fall out of several other manufacturers cartomizers. This points to more than just different production runs of the same thing, as when you examine them closely, the internals and
threads etc are visually different.
Another thing is that the genuine VK cartomizers seem to last far longer refilling than do the other off brand types.
Another quality control issue you'll discover with off brand cartomizers is getting the atomizer centered in the cartomizer (you'll note this when you open one to refill) most off brand cartomizers require some adjustment to be centered, and a lot of times they keep springing back and you have to play with them a while, and some have the batting put in offsides so you cant center them properly at all. Having your atomizer off center causes it to heat the exterior of the cartomizer to an uncomfortable level, and usually causes premature failure of the cartomizer.
VK cartomizers are a little higher than some of the off brands..but just like cars..you get what you pay for. Why drive a Gremlin when you can have a Toyota for a few bucks more?
I'm a cheapskate..I endeavor to get the most for my money with every purchase I make. To date, nothing has topped genuine VK cartomizers, and the only reason I
buy *any* from anyone else, is because Customs ate all of Steves 60/$100 empties...and we all know that if you experiment with flavors, you'll need some empties

.
I anxiously await V4L's return of bulk empty cartomizers...im gettin sick of these chinese rejects (they all come from china, but these are like seconds) I keep having to
buy to satisfy my empty cartomizer needs. They burn prematurely, they taste like baked ...., and the batting looks as if it was thrown in them from a distance of 30 feet. Help us out Steve, Hook us up with bulk empties! Get on his .... Mark, make it happen!