If this works as well as it appears to, with no slippage between the original and zipped-on tyre, this would be a great product.

When you're riding a bike on the road with mountain bike (or off-road) tyres, you lose a lot of energy, with the tread on the off-road type causing a lot of drag - which really adds up over a distance.

So, to be able to simply change your tyre configuration as you go off-road would be a great solution. But there'd have to be absolutely no slippage between the two tyres for this to be effective. As a mountain bike rider, you rely on a sure grip.