its pretty good the only thing is it is easy to take out chunks on the rail. Mine has a couple indents and burs but not rly a problem u can just fie them down
i havent done any yet (on rails or pvc), but i think it would be easyer on a shotgun rail (pvc, or metal) because it is round so it is easyer to drop your tip of the one ski and drop the tail of the other.
i think hes just talking about gripping the rail like the "gas pedal" way or whatever you want to call it. i dont think that it would be bad on PVC you would probably get a little more grip on metal but pvc is softer so it could be a wash between the two. i only have pvc on my boxes and i havent had a problem gripping them enough to swichup and spin off and on