Very good, highly recommended
If you are caught with a puncture, and no spare wheel that is a good solution – or you are not able to put a spare wheel on (like my wife)
I had an Audi A2 in which I was able to take the small back roads to avoid the m25 daily car park situation in with that car I used a 2 year period over 5 canisters on even so much punctures – some roads are just crap – and yes tyre dealers will not touch a wheel with the gunk in it, sometimes they charge you extra. And no you cannot repair one after you have used the stuff
At the end I bought a spare wheel, and used that one never!!!! – sods law
Last week I used a canister on a puncture, it got me home, and to the tyre shop – again no spare tyre – a lot of new cars do not have spare tyres- so yes always carry a canister with you for these emergency situations -