I've tried a couple (albeit two or three years ago) and was rather underwhelmed by their performance - I also found that putting on other things such as wireless networks and cordless phones had a negative impact on the signal - it looked like I was using a set-top aerial!!!
Can you not run an RF cable upstairs from the Sky box (it has 2 RF outputs for this purpose)? If you do this, you can then get a MagicEye, which will transmit the remote control info across the RF cable as well, enabling you to change channels from upstairs.
I did this by running the cable through the outside wall, and then back in to the room above (obviously this depends on the layout of your house), as the missus didn't want the cable running up the wall...
We're on the last freedom moped out of nowhere city and we haven't even told our parents what time we'll be back.