Do the others work the same way? I get the impression that they come before the receiver (straight from dish) and capture the raw data stream. So..you wouldn't have to change the channel on the receiver..the PVR would do the tuning...or am I incorrect here?

I'm really a newbie at this, so forgive the newbie questions. I just recently had DirecTV installed.

What other considerations should I make when selecting the unit to get? Aside from the dual tuners / dual recording thing and picture quality degradation thing...is there much of a difference in functionality?