How many punctures have you had in any one two year period?
In my case, I've had one puncture in 18 years of driving.
So spend a guaranteed £200 for the chance of saving £300 per puncture over two years?
Compare it to car insurance.
People whinge about £1000 policy but it gives me a chance of recovering 70 times my policy in one year.
I know the periods aren't the same but the value of motor insurance is orders of magnitude better.
I'd rather take my chances.