I'm still using my 650 as my daily driver, and while it does meet my minimum requirements, the app gap continues to be a bit of a drag. Its always annoying when my friends of coworkers are all playing a game (PUBG Mobile) or are using a workout app, and I'm never able to join in. So W10M is great as long as you don't have friends, lol.
Another constant issue are all the bugs, they're not a big deal at first, but they seem to get worse overtime. These bugs include: Constant restarts, loading screen taking way too long to load simple apps like the calculator, Bluetooth connecting and disconnecting when it feels like, ringer randomly turning on after I turned it off (making my phone ring in the middle of meetings -_-) Excel mobile not recognizing that I have an Office subscription and not allowing me to edit my sheets, etc.
Its not all bad though, I enjoy how well Excel, One Note and the Office Suite overall sync to all my devices. The layout and start screen is still the cleanest and most functional I have used. Cortana is useful for what I need her for, and I enjoy the benefits of being part of the Microsoft Ecosystem, allowing my data to be accessible from my phone, PC (Personal, Work, Wife's PC) and XBoxOne.
Sometimes it gets exhausting being a W10M user, but the benefits out way its downfalls for now. Looking forward to Andromeda though.