A few bits of trivia about PVC glues:
1) There is no technical reason the glue, or the primer, cannot be made in any color of the rainbow. It's only a desire for good workmanship and easy inspection that folks use 'purple' primer, with a glue colored to match the pipe;
2) PVC glues DO come in different 'bodies,' or weights. There's 'light body' stuff that is thinner than water, 'medium' which is what most is, and 'heavy,' which is as thick as maple syrup on a cool day. Which one is 'best' depends on how large of a gap you need to fill and how hot it is outside. The goal, of course, is to have just enough 'working time.'; and,
3) Only the clear stuff carries a UL lable for use on electrical work.
Enough for the facts
Now, for my opinions:
I am not the least bit concerned whether the glue has a UL sticker. I'm only interested in that it be a PVC glue. Actually, I've encountered numerous PVC runs where the glue didn't hold, or wasn't used at all, and I didn't see any harm done.
Which is an attitude that contradicts my personal practices, where I've grown to prefer using the clear 'pipe cleaner' as a primer, followed by glue on both pieces to be joined. I want MY pipe to stick together. It just seems 'right.'
I'll use the clear stuff - which is thinner and dries faster - in cooler weather. I'll use the gray stuff - which is thicker and gives me more 'working time' - in hot weather and with large (2" and up) fittings.
While I don't apply glue to the assembled joint, I like to see a nice bead of glue around the joint after I push the parts together.
Finally, the stuff does need a bit of time - maybe 30 seconds or so - to really set up. Plumbers are told to wait at least 15 minutes before turning the water back on. Those parts may not move around any more, but the bond is still forming.