I have Safari, and find it to be a poor value. Here are a few reasons
(1) you can't read books in your browser while offline
(2) many publishers don't contribute to Safari (Springer, MIT Press, etc)
(3) publishers that are technically on Safari don't publish their whole catalog (Wiley)
(4) Publishers that are on Safari, and do publish their whole catalog, may take months, a year even to put their books online (Wrox). (5) A lot of the books in the catalog are from Packt, which I consider noise.
So, while I do have Safari, I use it as a last resort and buy the DRM-free PDFs from publishers that have then (Manning, Prag Prog, etc) even if they are in Safari.
This past week, my account got corrupted. I lost about one years worth of Playlists that I put much effort into curating. All gone. Support was able to get me a CSV file of a known good state, but its going to be a PITA to manually recreate everything again. I might not bother.