I've never replaced a keyboard yet because the letters have worn off, they usually last longer in this house than the computers they came with
At the moment I'm using a logitech but the annoying part for me is it's slightly smaller than the previous one - although I'm not a touch typist I do seem to hit the wrong key or two together. My advice would be to check the size carefully as they may look the same but might not be, apart from that if you go through them that quickly then just buy a cheap one when you're next in Tescos.

Jan