Paul Terry wrote:
OK, let's look at a specific example: Bus to Richmond station, SWT to
Waterloo, tube to office. The same coming back. That costs £8 on a
one-day Travelcard. Using Oyster pre-pay, the two bus journeys would
come to £2, the two tube journeys would clock up £3.40. Add that to
the cost of a day return on SWT for the bit not covered by Oyster,
which is £5.90. Total using Oyster comes to £11.30.

Have I miscalculated, or does Oyster strike you as "not a sensible
option" for occasional use when it pushes the total cost to nearly
50% more than a travelcard?

One of us doesn't seem to understand what the word "option" means. I
take it to mean that one can use it when it's to one's advantage to do
so. It sometimes is (even if not here) so it's a good option to have.
Had the post I was responding to said "it's not sensible for this to be
the only option", then I wouldn't have any reason to disagree. I'm sure
there are plenty of occasional travellers who can benefit from Oyster.