Evidently, the 510 Mega cartomizers from Drew vary from time to time. The ones I received 3 weeks ago are the aluminum type and measure about 3.0 ohm resistance. I notice the ones on his site now are 3.4.
These carts are about the same physical size as a regular one. Actually, mine have a wee bit smaller diameter. I say that, because the plastic tips on my other ones will not quite fit in the tube of a mega. The aluminum threads are not completely free running like my other carts, and it is necessary to twist them a bit firmer to get them to seat all the way down on the battery.
The mega cart holds more juice because it has more filler inside. In other words, there is less unused space inside. If you look through the small tube in the center of the filler, you will see light all the way through the cart, thus giving them a nice, easy draw. However, the small tube in one of mine was off center and somewhat restricted. I managed to get it centered and cleared out, so now it is working ok.
I have not cleaned any of mine out yet. Maybe I should. I rotate to a different refilled one each time I charge a battery, so none of them have had a chance to go dry. Then too, I try not to crowd them too much during use, so as to give the filler enough time to wick.
All in all, I have had fairly good results with cartomizers. I have been using them for four months and had to learn my lessons the hard way about burning the filler beyond use. Fortunately, I do not require tons and tons of vapor and a tremendous TH to satisfy me, and the carts are good enough to do the job.