Thanks all.
The screenshot isn't clear but the pricing you can see in my OP is for a return; not one way.
I was posting very quickly as, like many others, I had places to be this morning, but I have now amended my screenshot to be a valid comparison with a return. The saving is over a third off, i.e. better than a Railcard holder would get if booking with SWR for that journey.
In this case, you should wait because there is a good chance Advance fares will be released, however it is worth considering purchasing elsewhere than the SWR site, as SWR charge premium fares for some journeys, which some sites will circumvent. I had a quick look for 9th February, and found the forum's site sells tickets for a couple of quid less than SWR, which is a much smaller saving, but still worth considering.
Furthermore, using the forum's site helps with the forum's running costs
