I was facing the same choice but decided on the Buzz Pro. The stacked batteries don't concern me with the safeties that are built in. I think you would have to work pretty hard to get it to, in the words of battery manufacturers, spontaneously disassemble. My biggest deciding factor though was ease of use. This is highly subjective but, for myself, I don't like to fiddle with things to get something done. The Buzz Pro is simply reach up, turn dial, vape. I can do it pretty much anywhere, anytime. The ProVari required more of my attention to get anything accomplished and I had the vague feeling of entering cheat codes on my old playstation...
The choice for me came down to: do I want a mod that gives me "slightly" more features but requires a higher degree of interaction or do I want a mod that simply works unobtrusively in the background? Just my two cents.
- Xeno