I've done a couple. I treat it much more like a " I'd like that thing to exist" rather than a "sell me that thing" sort of proposition. A little forethought goes a long way, and so long as you are not buying someone's super industry breaking tech, you generally do fine. Heck, I got a phone off there, the jelly-phone, and I expect my atom phone to be shipping soon. nothing overly special, just a design that needed some funding to make happen. I've also done two coffee makers and the firefly firesteels.