Well, I'm gonna be the dissenting voice in the crowd.
I'm using Sustaretard and for 1-3 days after the injection, I feel as if someone has shot me in the ass with a fucking gun. Someone on another thread said that you gradually build up an immunity to the pain (not just a tolerance) so each shot hurts less and less. We'll see. Did my 3rd shot last night which means I'm back to the site of the first shot.
Anyway, everyone reacts differently to the injection. Just make sure you stockpile a bunch of excuses for the limp and pain before you get sore. But I know my girlfriend will catch on to this if I have a sore ass for the next 7 weeks.