I’m not sure what you mean by ‘filtered guide’. If you mean looking just for movies or that kind of thing, then that’s true.
The DVD plugin will burn a data disc for those people that have Divx-capable DVD players. I’m sure there are other reasons but that’s the most logical.
I’ve evaluated most of the PVR software out there and BTV has far superior video quality. I played with Sage for a few weeks but could never get it to look as good. I also find the ‘ease’ of installing Sage add-ons laughable. Those .jar files often conflict with each other and cause Sage to lock-up. I suppose if you like like the pre-packaged replacements as they are then you’d be okay but I found all of them to be ghastly in one way or another.