I thought only the worst when I saw the title of this thread...

I have used it, it may work with repeated applications like the directions say, but after 2 days of applying, waiting for it to dry, and reapplying, I finally went and got a tube of Ruscoe sealer, it worked just fine, and on the first application.
The crack cure does have to potential to seal something you can't easily get at, but I think it is more like the cans of K&W Block Sealer you get when your car blows a head gasket. I never had one seal anything, except the cores in the radiator

. Better to fix it right the first time, than keep messing with it for days, weeks, ...