Sorry if this is redundant but do you punch 1 hole or 2? I'm confused because I thought they needed 2 holes but it sounds like now everyone is just doing 1?
I've punched up to 3 holes in cartos before, and had them work beautifully. It just depends on the VG content, really.
As for methods, I have a saddle valve that I've been using, but it likes to slide down the side of the carto a lot of the time. It worked great like the first three or four times, but now it's just a hassle to use. Last night, I slotted one with my Dremel. It worked quite well, but now I have a metallic taste to my vape, which is not so good. It could just bee the carto though, I've had that before. Phiniac sells a sweet punch on their site. I think I'm about to order one myself.