What Dunster said about how they work. Only problem with either the velcro or the zipper system (similar to velcro but zippers instead) is that with both you have to still either sew or pin baste the backing to 2 leaders and top if you don't float it. And while you can take a quilt off and put another on easily--you can do that only if you have another set of velcro/zippers!
I bought the Red Snapper system in May and LOVE it--so easy to use despite 2 complaints I'd heard about it--1) that they are too hard to use as rubber is too stiff to get snapped on--was told they would loosen up with little time (did) and that you could use a hair dryer to soften at first if still too hard to use (friend with RA did this and says it works) and 2) they use too much fabric to attach--NOT! I use no more than when pinning! My set for a 14' table was $80 and WELL worth the price--suggest you check them out.