So while I still liked Windows 10 mobile overall (on a 640 xl), I've had a few problems (mostly documented on these forums) and while they mostly seemed to sort themselves out, I was starting to think it would just be easier to drop it and go back to Android. 

Then a few days ago I got the anniversary update... initially it looked like this was also going to be a problem because it kept error-ing trying to apply update, but after I removed a bunch of apps and moved others to my SD card to clear some space (which proved nice and easy to do) the update went well and I must say I'm loving it now!

Groove music actually works properly now, replying to text messages direct from the notification is nice, love the music controls on lock screen, I'm really liking the way cortana behaves with a bluetooth headset (it might have always behaved like this - but I only just got a bluetooth headset lol) and everything just feels a little smoother and more polished.

Likes like I'll be sticking with my 640XL for now... :)