I bit the bullet and, with some trepidation after reading forums for months, spent Saturday setting up Photos on my iMac and MacBook. I set Photos to create a new empty library for itself on my MacBook. I made sure I had safe backups of our Aperture library on the iMac, then let Photos build a new library for itself from the Aperture library, then took a big breath and turned on iCloud Photo llibrary on all my devices after purchasing enough iCloud server space. I've been pleasantly surprised. It's taking a long time to upload all our photos, of course, but right away they began appearing on the other three devices (MacBook, iPhone and iPad). Each of the iOS devices uploaded their Camera Roll contents. My Aperture album/project structure is preserved. I can already see the convenience factor. It's huge, much simplifying my previous clutzy workflows using PhotoStream and iTunes. Photos has very limited editing tools, but they are enough for most of the post processing I do these days. I don't need much more and hopefully Apple will add those with time. Meanwhile I've got Aperture if I need more editing. So, so far so good.