Just re-read - you've seen that Advance fare!
The off-peak is valid as you are effectively travelling away from Reading (and Reading fare is cheaper anyway, so you wouldn't buy and travel short).
Off-peak is different depending on where you travel to
Thanks ChrisB - I didn't want to tie myself down to a specific return service so bought an off-peak return. Paid for on-line and collected from the
TVM▸ at the station.