Just a quick update on progress.
I started with the smallest 2.5mcg dose and although I was getting something, it was really just a semi and so I was concerned as to whether increasing the dose would improve rigidity or just prolong it.
Well, I had a slight issue as I was told to inject alternate sides with each dose and on my last 2.5mcg injection, I was trying to inject the left hand side and I am right handed (I still haven't plucked up the courage to get my wife to do it lol). Anyway, I was convinced that I had twisted the floppy shaft and maybe injected the wrong spot - it didn't feel right and it was uncomfortable rather than painful.
Anyway, that put me off for a bit, but last night I tried the regular right side with a larger 5mcg dose and I can confirm that it definitely improves rigidity and a little manipulation also got the glans nice the firm and purple - good blood flow.
The erection lasted the same time as before - about 20 minutes and was definitely usable!