As a one off, I agree. Auto top-up, OTOH, avoids having to worry about
running out of credit. Which can be a bit of a problem if you've just
boarded a bendy bus. (Not happened to me, but people have been
prosecuted for inadvertently running out of credit on a bendy bus.)

Well, that's their defence at least...

Well, if they're going to have a policy of ignoring the penalty fares
system and simply prosecuting at first offence (which it appears to me
that from time to time they do) then running out of credit is rather risky.