Dunno about deleting stuff if you don’t log-in for a month, but I would imagine that probably would happen.
Yeah, any stuff you download for offline is only while you are a subscriber; you are not buying the music permanently.
I am currently using Spotify premium having signed up to their 3 months for 99p offer.
I like it, but there are times when the app on my Sony phone doesn’t work and I end up having to restart the phone. Can sometimes take a while to download stuff too, even though other stuff feeds quickly. Most of the time it works fine.
I keep meaning to try other services to see how they compare.