Well, the 435 has been given the blessed position of being officially supported for Windows 10, whereas the 635 has not. That alone is a good reason to be very happy with your purchase.

Any 635s...

Yeah, the 635 has a software navbar. That seems to be the key issue for these devices.

The 435 has a hardware navbar (edit: and 480x800 resolution instead of 480x854).

My Lumia 635 also automatically downloaded the Anniversary Update. I wasn't even on the Insider program at the time - after using Insider to obtain the initial upgrade to Threshold 2, I left the...