I used both of the £1 for a month offers. Last year for The Outer Worlds, which was a disappointment, and again this year for Wasteland 3 and Ori 2, which were great.
I'll subscribe again when Microsoft publishes another game I really want, otherwise it wasn't a good experience. I had issues with downloads repeatedly restarting and wasting days of my subscription. Patches for Wasteland 3 were inexplicably late, arriving about a week later than the Steam version, even days later than the console versions.