Pics would help. I'm not sure your background with plastic molding, but roughness is a bit hard to achieve, but they due get some texture molded into car parts....generally very smooth feeling.
Here are some pics that may explain what I feel about the plastic itself. I actually found a set of feeler gauges left over from tuneups with points. For those younger than my socks, this was before electronic ignition! There is about 0.020 clearance between the cradle and the side where the "screw stop" comes in so there is very little space to add friction.
Other than this, the total setup is good enough to set scopes, clean etc since the pin I added allows more pressure. The current screw vise pads will hold rifle securely enough for this as well. Its just the cradle locking system is not very good and slides easily downward with very little pressure. The added bonus of the Wheeler Reticle Leveler helps offset the defect that I perceive. But the pins solve it well enough.