Powerline Network Adapters - Anyone use it and are they any good?

I have a E4200 Dual Band router in my home office and find that the wifi network signal is not that great to my Apple TV and Blu-Ray player. Instead of getting a wifi repeater, I was thinking of looking at a powerline adapter.

Does anyone use this and what type of speeds would I be expecting and what things should I be careful of?

Thanks