nothing. the sandisk extreme is supposed to be a good model. it has toggle nand and sandisk is part owner of a nand fab so they should be able to get the pick of nand. the one thing is it uses a sandfoce controller so if you are doing stuff with a lot of incompressible data beware of that. amazon.com is selling the drive for $80 usd which is the equivalent to £50. im in the US so i cant really recommend anything with a specific price because i only look at US websites.