I've just got one of these, and while it appears to work fine most of the time, I've noticed a weird screw-up from it when something outside of NPVR tries to detect what tuners I have installed (specifically DVBGuide or EPG Collector).
When they do this - just the detection part, not the tuning/collecting EPG data part - they cause the data stream being delivered to NPVR to get interrupted. That either black screens Live TV or breaks any recording in progress.
Has anyone else noticed this? I'm running 32bit Windows 7.