I have and love my Pyrex RSST. It's one of my go-to RBA's for an all day vaping set up, while I'm out and about or at work.
With regards to the glass tank, as you may already know, the design is completely different from the plastic tank design. So if you have a plastic RSST, and you buy the glass tank, it will not work. The glass tank is a sleeve, secured by the top and bottom cap's pressure when screwed together via the center post. The plastic tank is a cup that fits over the bottom cap.
With leaking, any genny will leak if you put it in your pocket upside down, or leave it sitting on a table horizontal for a length of time. Other than that, you don't get leaks. Especially true if you use the fill hole plug. I use to get that drop of eliquid that would leak out of the 510 connection with my RSST. I fixed that issue but taking a small piece of Teflon tape (plumbers tape) and wrapping a 1/8" strip around the bottom of the center post, then screwing it to the bottom cap to make the 510 connection. Since doing that, I have gotten zero leaks in the 519 connection.
There are ways of leak-proofing gennies. If you use wire rope wicks with a mesh sleeve, you can plug any other deck holes and still have sufficient wicking. That's what I do with my outdoors/pocket gennies. They spend most of their time in my pocket. Either on their side, or sometimes upside down if I'm sitting. Some people also use hollow mesh wicks to the same effect. Or use wicks sitting fairly loosely in the wick hole. I haven't had a lot of success with the latter, but I'm sure it's just for lack of trying.