This has come up a couple of times recently. They seem to work OK, but you have to have all the pipes that go into the fitting in place because once you heat the fitting, all of the solder liquifies. I'm think especially of a tee, but elbows and couplers have the same requirement. I personally think its a gimmick aimed at DIYers who think it will make sweating joints easier. I can't see the big deal myself, what's the big savings?