My friend runs an older 250 and a newer 250 and we can't tell any kind of video quality difference. And again neither have had failures and mine have run 24/7 for the last several months recording on both simultaneously almost constantly. Not problems yet (fingers crossed?)
The 350 has the FM tuner which is kind of nice. The output is not exactly TV out but MPEG2 decoder out only. That is nice since all decoding is done by that and not the CPU (so you could get almost no CPU usage when watching an MPEG2 file). Snapstream does not support that either. But you can try that with the WinTV app.