I've not seen the pattern ones so cant comment but I have struggled to find a decent used one. They tend to get a bit brittle with age and the strap that connects the top an bottom halves together breaks very easily.

I broke the last one I bought un wrapping it, ended up using some black RTV to glue it to the swinging arm!!! Bit of a bodge but it works a treat and the chances of finding a good used one are pretty slim.