Got these a couple of days ago from Asok (thanks). I was using a set of fiberglass kness, (I'm sure everyone can tell who made them). The FG knees were tight around my knee and didn't allow much bending. Got a good deal on the vac-formed so I gave them a try. I used Asok's tutorial and they came out great, IMO. I think they look more size accurate, they flex nicely, and are a lot lighter.
Because of the plastic, I had to hit them a few times with filler primer and sand them down, check them and reprime/wetsand.
The pics show the comparison. The vac knees are on the left in both pictures.