The thing is that Colin Percival has done genuinely novel computer science, real heavy lifting, to make both strong encryption and smart de-duplication possible in the same service.
So far as I know, nobody else has done that.
In practice tarsnap is cheaper than everything else because of the dedupe.
Well you have me there. I'll fall back on the fact that Colin's code is available and that he's published papers covering all the maths and computer science that leads up to being able to dedupe without sending stuff to the server or decrypting on the server side.
So far as I know, nobody else has done that.
In practice tarsnap is cheaper than everything else because of the dedupe.