I have used stretchers only for about 18 months. (Jes and home made leg strap. Since the Jes broke (1 yr ago), I have only been using the leg strap and some manual stretching in the shower.
Stupidly, I didn’t measure my start length, as I didn’t believe it would work (yes, silly). Because it did work.
Girth:
I definitely gained! (Just noticed this one day whilst masturbating, haven’t lost this gain)
Curvature:
Mine’s a bit to the left, and it seems a bit more straight now. Still curved, but this has never bothered me to begin with.
Length:
Yes, I gained. But I don’t know how much.. I would say 2 cm erect, 1-2 flaccid. (I base this on measurements I made when I was in my early twenties (now 32). So not 100% reliable)
So gains are modest, given the fact that I stretch 7 days/week, for at least 5 hours/day. Since I wear it to work, the stretch is mild to avoid slipping off etc.
I have started to take measurements now, to monitor any new gains. Assuming I have had my newbie gains long ago, any gain now will prove stretching works.