i punch mine. but hey whatever works right. The reason i chose to punch is this and understand i may not have a clue what i am talking about its just a feeling. Drilling, you lay said carto down and push drill into side, ok easy enough but having used a drill since i was a kid i can tell you its easy to slip. I can just see me now down to my last carto trying to drill, push to hard and the bit pops through the other side. destroying the air tube in the center and maybe even trashing the coil.
Slotting with a dremal, well those buggers move really fasy (even the cheap ones). Would be way to easy to slip and cut the carto in half or damage the coil. Even if all of that did not happen, you now have metal dust in your carto. I dont know if that could or would short the coil, but i certainly would not want to be vaping it into my body.
Nope a punch is the best way for me. For a mere $6 i bought a saddle valve. It is easy to use and the chance of a mishap is small. Down the road i am intent on buying one of them there fancy carto punches i hear them city fellers talking about lol
Like i said thats just my nickels worth, but use what you got to. Hey man if i had to i think i would chew a hole in the side of the carto to get my vape on lol