The Hauppauge MediaMVP - the hardware used for the Sage Extender - is a pretty limited device.
It only supports composite and svideo outputs. Audio is two-channel analog only. These are limitations.
On the other hand, it is cheap (relatively speaking) and small. It has mpeg2 decoding in hardware - so playing an mpeg2 requires no processor intervention on the server. For other types, the server (Sage in this case) needs to transcode.
I think it stands out from most of the other networked media players. While it's not fancy and doesn't have high-end outputs, the hardware works quite well. Given the price, I think it can be a much better solution (not for everyone, though) than many of the other options, especially those that essentially require a computer for each location (local or remote). Hauppauge chose a simple, relatively inexpensive solution. They also seem to stick behind their product better than most of the other networked media players.
If you have a PC for each location, the Sage client works well (if you want to stick with Sage). I use the Sage client in another remote away from my PVR machine (running Sage) to control Sage. It can play back everything, too.
Sage PlaceShifter can be used to stream video (recorded or live) over the internet (client is intended for LAN use). This should work about like the SlingBox. You pay $30 on top of the cost of Sage for each license - you need a license for each connection you want to maintain. This, by the way, may be a good solution for people who have been talking about using something like a SlingBox to monitor security cameras.