I have a 640XL. Win10 upgrade was crap; drained battery twice as fast, SMS is a mess, sluggish response. This past weekend, got a BITLOCKER blue screen and had to re-image it. Went back to 8.1. I should have never upgraded it.
I'm using my other Win10 (one I take for traveling) and seriously thinking of ditching my Windows phones. In all my years with an iPhone, never had it crash on me. Just hate spending $1000 on an unlocked phone though.
Windows 10 Mobile is such a mess. I wouldn't recommend it at all. It feels like Windows 3.11 in an era of OS/2, MacOS, and AmigaOS.