I had one, bought it at a local sexshop and they only had the "normal" insert available.
Meaning no texture inside, just smooth surface.
It felt really dull and was rather loose. I admit, I have a small dick, but still, compare it to a tenga which was so tight I had to work my way in with fingers first for like an hour.
Had my way with it for couple of times and then I threw it in the trash, money well spent.
If you buy one, get the ultra tight.