I've never used one because I don't like the looks of them. To me they look way too complicated and bulky. And prone to breaking.
gzg, I ABSOLUTELY understand your concerns... Read thisthread I wrote over the summer:
http://www.huntingnet.com/forum/tm.aspx?m=1687790&mpage=1&key=pass%2csalt& amp;#1687790
To answer the original question, the slide is supposedly made of Teflon; there shouldn't be any friction issues there. Nothing else in the mechanism or linkage should slow anything up.