Ditto on the clear pvc for hard pipe. I've never glued spa-flex, so I can't chime in on that.
Just remember to:
1. lightly sand the two hard pipes in the areas to be glued. This gives the glue a better "grip" on the pipe.
2. wipe the area that you just sanded with a clean cloth to remove dust
3. coat BOTH the male and female pipe sections with the glue
4. mate the pipes and give them a 1/4 to 1/2 twist. This will smear the glue even further and give you a good coating.
I've never used the primer, and I've only had 1 joint ever have a slight leak.
If you're doing elbows and whatnot that you need to have at a particular angle, I recommend doing a dry fit, and marking both pipes with a pencil or sharpie to show the aligned position. Then when twisting in step 4 above, just twist until the two lines line up. Voila!
Apologies if you already knew all this.
P.S. Having plumbed two basement sump/refugium rooms, in retrospect I would use spa-flex whenever I could. It would've been much easier on me for all the angles/turns.