it looks like a good idea but they are very heavy footpegs because of all the extra connections you need to make it removable,
also you only get the one side so one footpeg will weigh nothing while the other weighs a ton.
used to work in a bike shop and the rep bought them round to try to get us to stock them but after you've felt the weight you dont wanna go near them!!!!
and as you rightly say mate... when bikes are being lifted what goods a disc lock!!!!