I used to believe that USP 99.5% was cleaner or safer. Perhaps it is. It was my choice initially.
A lot of them used to say USP. I am no longer convinced that that pharma USP grading really means much at all anymore (if it ever did). I do use both. Which ever is convenient to acquire will do for me.
Anyways, I prefer to no longer smoke for my nicotine nutrients. I know what smoking did, and I now know what
vaping does for me. And I trust and prefer VG more than PG for me.