I use Safari heavily and I've been hoping some sort of competitor would come along.
It's not that that I dislike Safari, merely that I expect competition would push for a better product. The interface has barely changed in as long as I can remember with the same old clunky flash and limited search. It took years for the mobile app to go from horrendous to tolerable and it remains quite bad.
Giving 'Online' the same visual style as 'Flow' would be a start, but they seem to be keeping them separate and beyond the visuals I found Flow to underwhelming and frustrating even. I cancelled my Flow subscription despite being offered a deep discount as some sort of early adopter.
Meanwhile, Inkling is great is several ways, but lacks the critical 'all you can read' subscription option.
Kind of disappointing that the new service is separate from the existing 'Safari Books Online' service. I'm grandfathered in to the $9.99 5 books/month plan right now. Jumping to $24.99 for a new interface hardly seems worth it.