In message , Paul Corfield
writes

The button only says Alternative Fares - that does not mean cheaper. In
many cases I have looked at the alternative fares can be cheaper or more
expensive or even have several sets of more expensive options.

There's also the difficulty that the Alternative Fares often don't show
practical alternatives that can be both cheaper and faster, unless you
know exactly what to type in.

For example, Lewisham (DLR) to Bank is £2.30 (£1.80 off-peak), but the
considerably faster SouthEastern service from Lewisham (NR) to Cannon
Street is cheaper at £2.10 (or £1.70 off-peak).
--
Paul Terry