Since it's recently arrived in the UK I thought I'd give Deezer a quick spin on the 15-day Premium+ evaluation.
Adding albums to 'My Deezer Library', all was well until I soon hit a roadblock and it would refuse to accept any more.
Checking on deezer.com I find that Sonos stores its 'My Deezer Library' in a 'Sonos Track Library' playlist with a ceiling of 400 tracks.
The Deezer FAQ says that "your playlists are limited to 500 tracks" but an additional 100 tracks is neither here nor there. The entire design seems completely compromised if one can store no more than a few hundred tracks in 'My Deezer Library'.
What's more, playlists added to 'My Music' in deezer.com don't show up anywhere in Sonos. The 'Playlists' branch in 'My Deezer Library' remains stubbornly empty.
Members with more experience of Deezer may be able to tell me I'm missing something obvious?
EDIT: FWIW the Deezer FAQ
is evidently out of date, though it does confirm that Deezer playlists are not visible in Sonos.