This one really works well.  I've tried others to no avail.  This one does just as promised, and is worth the price.  I needed 5 by 5, so was able to get a 5 by 8 and use the extra on some throw rugs!  I cut mine about 2 inches smaller than the rug all around...it lays better that way.    

Pros: Easy to trim with scissors, give rug a nice soft feel to walk on
Cons: None