These inner tubes have done a good few trips to Wales, France etc. and throughout I've never had a puncture... but neither did any of my mates using normal inner tubes.
...However, after a short period of a few months of not using the bike (storing it in my garage), I got it out to find both tyres pretty flat. Not needing a top up flat , which was all my wife's bike on normal tubes needed, completely flat.
Before pumping them up they needed a fair amount of pressure applied to free up the presta valve, which I half expected as the goop had probably settled from storage. However when I started pumping up the first tyre the valve casing snapped completely off, with the end stuck in the rubber pump seal.
The bike had been sitting in my dining room overnight so the valve didn't go from cold to hot too quickly yet the valve had cracked around the circumference which made it snap off and vertically at right angles to the thread.
Although I personally have never had a puncture with one of these tubes, a friend of a friend did which resulted primarily in him and his bike getting covered in green goo. He then had to borrow a normal inner tube from one of the guys he was with to get back to the car as the goo failed to plug the (small) hole enough to maintain pressure.
For the messy hassle, additional weight, and the expense of a replacement when these don't work properly you're better off using normal tubes and a packet of scabs, which is what I'll be using in future.
Great idea, just doesn't work as advertised hence 2 stars.