I tried it this morning from St. Albans City to St. John's Wood (Jubilee line, zone 2) and TfL shows a charge of £11.70 for the journey under 'today's travel'. By comparison the single rail fare for SAC to WHP would have been £11.90 with £1.70 extra for the tube (total £13.60 giving a saving of £1.90).
Assuming the fare is the same in the other direction, the return for that journey would be £23.40 with contactless vs. £20.10 + £3.40 = £23.50 with separate rail + tube.
It looks like single fares might be cheaper with contactless but symmetrical return journeys about the same (kind of what I was expecting).
Will be interesting to see how train + tube journeys via St. Pancras are charged, particularly ones that could also have been made via West Hampstead avoiding zone 1.
Just looked at a notional trip from St Albans City to Wembley Central
via West Hampstead stations
Peak £10.00
Off-peak £5.80
So, avoiding Zone 1 would cost £11.60 with Contactless if both journeys are off-peak, as the paper off-peak return for this route is £14.00.
If someone makes this round trip and travels in the peak in only one of the two directions, Contactless would be much cheaper, at £15.80 vs £20.80 for the Anytime Return.
The occasional traveller really has my sympathy. Not only do they not usually know about ways to save money using split ticketing or Advances (not in this particular example, admittedly), but now they could also be paying too much simply by using the ‘wrong’ way to pay for their travel