Yup, I watched a guy work magic with the stuff at a show. I bought some and can't do squat with it. Well, I can seem to get it to work, but not nearly as well as the demo guy. He must have hundreds and hundreds of hours practice.
I'd use it as an alternative to buying a TIG machine or an expensive spool gun for a MIG for small projects or repairs. I even used a slightly different stuff for fixing pot metal pieces for collector cars. I'd rate it above using JB Weld for sure.
Overall, I guess I'd say it's really not bad I suppose. Just make sure that you practice for an hour or two on scrap before trying to work on something of value. If you get that "touch", it's probably pretty darn good.