I had collagen stimulating filler done a couple of years ago from a clinic based in Denver that has a Chicago location (if you DM me, I'll tell you who it was). The reason I went with it was because it sounded like the only filler that was promising permanent gains in the glans. I had the glans done first, with the intent to come back for a second session to do the shaft. After doing the glans, I opted not to move forward with the shaft as I wasn't happy with the results.
1. Most of the size was lost within the first month. I suppose some of this could be attributed to swelling that went down. Also, I'm told that the glans is difficult to enlarge with anything, so that might not reflect how the product would work in the shaft. Additionally, I was told that the product itself is not intended to stay in the body long-term, rather, it stimulates collagen growth while it's there, then gets flushed away.
2. After the first month, what was left was lines on the glans where the surface was hardened and thickened by the product. I really don't like this texture and this was the main reason I decided not to move forward with the shaft. The thickened glans surface looks unnatural, and because it lacks it's original elasticity, I think the glans is somewhat smaller when
Flaccid. However, the thickening does slowly seem to be going away. After 2 years, I'd say I still have at least 50% of the original thickening though.
So, the bottom line is that the stuff does have a long-life, although maybe isn't permanent. I would say that the texture of it is really not desirable though, so I'd recommend against it.