They work provided it is a small puncture and the tyre has not torn, burst or been driven on when flat. But they are really only designed to get you to a repair facility, not at all as a permanent repair.
I wouldn't touch them with a barge pole - using it will probably make your tyre unrepairable because it can't be cleaned off well enough to allow a proper patch to be used.
I think Hopkirk is lucky he didn't die before the car did - just asking for a blow-out.
They are get you home only goods. For the costs of buying the repair spray you might as well take the wheel to your local tyre repairers and let them have a look, if its a straight forward puncture then the cost will be about the same if its unrepairable then using the flat tyre spray would not have been be a good idea anyway. Its all about safety,good tyres on a car are important, especially taking into consideration the recent weather we have been having.
These inflators do work in most cases...but should be regarded as a temporary repair. No sensible person would use one and not get the tyre repaired/replaced at the earliest opportunity.
Hopkirk's "repair" idea seems like madness to me.
I had apuncture repaired last week(cost £10, including rebalancing). I asked about these kits and was told it is almost impossible to clean the tyre and wheel rim after so it affects your wheel forever aterwards.