I have noticed these cheaper OTA prices are now appearing in Google Flights search results, which is what's made me become aware of them sometimes being much cheaper than paying BA direct for the exact same flights.

But I am still not entirely confident using them, so recently I have made a few bookings direct with BA and then claimed https://www.flyertalk.com/forum/brit...guarantee.html - they give you a voucher of 2x the price difference if you are a EC member. But there are T&Cs and loopholes that BA can use to get out of it, so you need to follow the instructions precisely, and despite the name, it's not necessarily a guaranteed payout.