Ianigsy wrote in
ups.com:

I get the impression that while Oyster may be fine for people who live
in London and for tourists who only really want the central zones,
it's a bit more patchy for those of us who visit London once or twice
a year and want to go to specific places- but I'm sure it'll be fine
once it's settled down.

I think that's fair comment. It would be a little bit easier, of course, if
the obvious alternative for very occasional travellers - ie paying in cash
- weren't, by design, so astoundingly expensive in London.

--
Bewdley, Worcs. ~90m asl.