I've used em - it's really hard to get them on without getting fingermarks on the glue!
I've had reasonable success with them but don't think they are a true substitute to a feathered round patch put on with a tube of glue. But they will get you home and then some.
I usually chuck a tube if it has more than 2 or 3 repairs - more than that and the odds on a patch failure outweigh the economy of not getting a new tube. My old tubes? I chop 'em up latitudinally and fill little bags with hundreds of free little black rubber bands...
