Carl Beeth makes a spirited defence of the money usability of US dollar bills but this seems to me to be a case of “usability is what you know”.
Leaving aside the issue of the blind and partially sighted, the most important difference between US and UK money is that you are much less likely to hand over the wrong note in the UK. I suspect that Americans have a learned behaviour where they always check that they are handing over a note of the right denomination but in the UK because of size and (more importantly) colour differences this can happen in the subconscious. You aren’t going to hand over a big purple note (20) when you need to hand over a small blue one (5), even if you are not concentrating on giving over the correct note. After this, advantages of US bills don’t seem so significant.