Hey so I have one of 
I've run into an issue recently where one of the cartridges that I purchased for it doesn't fit properly (the cartridge in question has a flat mouthpiece that is longer than the normal round versions, and when you screw it all the way in it doesn't line up exactly flat to allow the case to fit over it). That's disappointing. I didn't realize this would even be an issue or something that I should have to look out for. It still works (mostly), but I think I'm also getting a lot of air in the draw as well which definitely affects the quality/useability.
So, all that being said, I think I'd like to get something that's a bit better quality and possibly more universal design. I like the pocket-able design of the current model and the fact that it's discreet. So, I'd just like to know what are some of your favorite models like this or what's the next step up in quality. Thanks!
Also,
USB-C please!