From someone who has had to use it, it works!
The instructions are simple and anyone can do it, you literally just drive forward so the hole is at the bottom, use a little plastic tool that comes with the kit to remove the valve core. Take the green goo and connect the tube to the bottle and valve then squeeze the whole bottle in then re-insert the valve core. Connect the compressor and pump up the tyre and watch in amazement as it actually inflates. Once the tyre was at the correct pressure I removed it and waited 5 minutes and re-checked the pressure. Still stunned at how this was working I carefully drove for a mile to the next layby a