Last time I changed my tyres, I found 3 lots of green splatter where I had punctured 3 times without even knowing it. I swear by the things, and almost never have tyre problems, despite being >20 stone.
My only bad experience with them was the occasion when I over-inflated one.
Don't do it! 
Quite why I was pumping it up in my living room I'll never be able to explain. The result was a snotty green version of the Big Bang that splattered the furniture, the ceiling, the TV, the carpet, Mrs Donger (while she sat reading the Sunday paper)

and one of our cats.

It was like the library scene in Ghostbusters where everything got covered in ectoplasm. The inside of the tyre looked like it had been painted green. Many months, perhaps a year or two later, we were still finding little green splatters on the underside of coffee tables etc.
Mrs Donger and I agreed that I would do all my bike maintenance in the garage in future.