We have tried muse which is inserted about 50mm down the penis with an applicator, it is not as bad as it sounds, I urinate just before inserting the applicator, it help it slide in and less chance of expelling the muse. We have tried it a few times; 1st and 2nd time, rock hard full erection that lasted about 40 minutes and I finished up pouring cold water on the penis to reduce the erection, everyone one was happy. 3rd time not as good, we were not as focussed as it needed. 4th time not as good as 1st and 2nd but think we understood why, avoid distractions and switch the phone off. We have experimented with different doses and more does not always mean better.
Read the instructions fully for muse if you get it, insert the pellet /cream, roll penis between hands for ten seconds, walk around and keep stimulating for the next ten minutes and it should then be working, the man should avoid lying on his back. Making love with the man standing also seems to give better erections. Don't rush things we thought the effect would quickly wear off but although the penis may go flaccid further stimulation may make it hard again.
Indulge in some intimate foreplay, stimulation is the key, if it goes soft go back to some more foreplay. They do advise using a condom to prevent the stinging for the woman slight stinging for the man but not painful.
I am just waiting for an appointment to see about getting the injections. Google flaccid intercourse, if you can master the technique it is well worth it, you might need to keep the windows shut.