My worry with this system is that you might be driving at speed unaware that your tyres are badly damaged. Did a quick search online and the AA seem to have similar concerns:
“Pre-puncture sealants
These are put into the tyre as a preventative measure either at the time the tyres are fitted or by injection through the tyre valve. The aim is to prevent air loss if a puncture does occur so the driver can continue the journey without interruption.
The seal is pretty much instantaneous after the tyre has been punctured and the concern is that the driver will have no idea whether there's been a puncture or not. A large screw or nail in the tread of the tyre will cause further damage over time and could lead to more catastrophic failure."
They go on to advise:
“Advice from tyre experts to users of pre-puncture sealants is to inspect the tyres
VERY often, ie every time you use the vehicle. If the pre-puncture sealant has been activated there should be signs of the sealant (usually white latex based) on the outside of the tyre. If there are any signs of this or of a penetrating object, then the tyre must be removed from the rim and properly inspected to see if it is suitable for permanent repair.”
I guess these systems are ok if you trust yourself and other users of the car to check the tyres on every journey.