I've always wondered about those, anyone have any BTDT with them?

Yes, best thing to do is replace the tire, yadda, yadda, yadda, but that's not always an option in the real world.
I have used these on automotive tires, downside is that you have to install from the inside of the tire so it's not an easy roadside emergency fix.

Many moons ago I did the "fix a flat" in a can repair for a slow puncture leak, rode hundreds of miles after that with no problems, but I wouldn't do that again unless I really had to.