I have not had any issues with my Panasonic DP-UB420. It larger than the Sony x700 and runs cooler. I have never seen it freeze. Never had to unplug it.
I didn't get the 820 as the 420 does everything I need. The DP-UB420 has a ton of features:
4K Ultra HD Blu-ray Player with Wi-Fi
www.crutchfield.com
I wish I got mine for $149 instead of $250...