The update is buggy and unstable.
Roku Model #: 4210X2 (Roku 2)
Serial #: 5F461N226680
OS Ver: 10.5.0 /Bld: 4208-04
I posted in this thread about what I did to recover my Roku 2 to get Prime working again. However, after a few days, the device began acting up: it became slow to respond to remote inputs to various Roku menus (not app or program menus) and eventually locked up. I was shuffling my programming app tiles on the Home page when things began slowing down and eventually locked up; the unit became unresponsive and locked on whatever menu I was on at the time. There were no error messages of any kind. I have never gotten any error messages since 10.5 was installed. A couple of "soft resets", done by pulling the power plug, got the device working again. And yes, I checked the remote batteries to make sure they were healthy; both showing full charges.
Last night my device shut down after watching an hour of Prime programing. After successfully watching the stream, I went back to the Prime main program menu page. I left the room for about 5 minutes and when I came back, the animated "Roku" logo was on the screen, playing its little ditty like it does when waiting for something to happen; this was not the usual Roku screen saver. The device was unresponsive to the remote and the white LED on the front of the device was off. I looked at the network cable connection and the green and orange LED's were lit (the orange one blinking). So I left it that way for at least an hour; when I came back, nothing had changed; it was still unresponsive to the remote and the white LED was still off. I ended up doing a "hard reset" after which it my device seemed to be working. I left it at that and didn't do any further "testing".
This software upgrade is garbage; it is unstable and unreliable. While it might work for some Roku devices, it doesn't work in all of them you still support. IMHO, a global reversion to 10.0 should be done until you can work out all the bugs in this current version.