i have been using tri-mix successfully for over 5 years. the concerns i have with it are, 1) need to keep frozen, which i just work around...but i am thinking of trying out 'bi-mix' which does not require freezing. it is said to not work as well, but I'll see about that. Also the standard tri-mix i have retains potency WAY longer than the pharmacist tells you. so don't go throwing it out past the 'expiration' date. just keep it frozen and it will be fine (IF you have any left!). 2) because you stay rock hard for a long time and there is no ebb and flow like regular erections, the rhythm is different with a partner. another guy can last only so long, so you have a hot time but hope his refractory period is not too long for another round, or you just switch to bottoming the next time (maybe take the top bunk to start, or do something else). 3) getting the injection in the right spot is tricky. despite the room it takes up in the shaft, the corpus is easy to miss when you are really soft. or maybe it's just very easy to hit a blood vessel. either way if you don't get right into the corpus the medication won't work. i have found that i can barely feel the needle in the 'right' spot.. so if the sensation is sharper i move the needle a bit. i also know if the needle comes out with a drop of blood in the tube something didn't go right. i think the answer here is to be partially engorged, which makes injection much easier and accurate, and allows you to binject much easier on the opposite-hand side (ie, left side of shaft if you are right handed, which they tell you is important to prevent scarring inside that leads to Peyronie's disease/bent erections)
the only answer i can think of here is to incorporate the injection into foreplay, which means involving your partner..or trying to get worked up a little before injecting so i'm not going into a totally soft shaft. i have been success at those injections in the past, but it is way way easier to inject when partly aroused. . i have been reticent to involve my partner to not interrupt the rhythm for him because he is so easily aroused... i hate to throw a speedbump in things. but it's just something we'll have to talk through . i know he will be understanding...and maybe hearing him voice that acceptance (even though i know it in my head) will be an even greater turn-on.