I've only had only one bad experience with quad injections. I've shot prop, tren, deca, test e & c, and sus in quads, and all were good to go. I've shot up to 2.5 cc in quads still no problem. I have a harder time with glutes just cuz I'm about as flexible as a brick. My TRT doc also recommended quad injections for self injecting. As for delts I've never done them. Mainly because my wife doesn't know I run AAS and don't want a bruise or anything where I pin to show when wearing a tank.
Not sure how much fat you're carrying, but if it's higher than most definitely use the recommendation of 1,5". And DO NOT FLEX. You will be hurting like hell. You want to be good and relaxed.