I flew LHR-AMM a few months back. I got the full 140 TPs for the route when crediting to BAEC. The seat was absolutely fine, as long as I can lie flat I'm happy. It does have an old school 2-2-2 seating arrangement which is fine if travelling with someone but a bit annoying if you're stuck next to a stranger (especially if you're in a window seat and have to jump over them to get out).
The lounge at AMM is pretty big, food options were a bit lacking but they did have a free bar.
I'd say go for it - obviously QR is much nicer but not sure it's worth paying thousands of extra pounds for.