Those are all good questions, however, there are unfortunately no good answers.
HA is incredibly inconsistent, so it's so hard to give you an idea of what to expect. I actually gained about an
Inch from 9 ml of
HA. But there have been guys who gained very little for 20 ml. My
HA felt so soft that I had to get it dissolved, but other guys have said it felt as firm as their natural erections. My
HA lasted about 11 months (there was a bit at the top that didn't get dissolved), but some guys have had it last for over 18 months, while others have seen it greatly diminish within 3-4 months. There are just so many factors at play here that even if you took the average results of all our
HA patients, it wouldn't really be worth taking too much notice of in terms of what to expect.
I think you'd be lucky if it lasts much more than a year, but unlucky if it was less than 9 months. It's probably going to end up feeling less firm than your natural penis, but how much less, is anyone's guess. In terms of gains, I'd say you'd be lucky to get 1/2", and to expect closer to 0.3" - 0.4".
Ultimately there is a reason it's not more popular, despite it's relative safety. I've seen some great results (Mato from Spain springs to mind), but more often than not, the collagen generating fillers produce superior results.
I don't think I'm familiar with Dr Mata.