current/voltage sensor?

Do a search on ebay for Arduino Current Sensor. I was actually just looking for Arduino stuff and saw the current sensor modules. I thought about getting this one:

http://www.ebay.com/itm/5A-20A-30A-Bi-Directional-AC-DC-Current-Sensor-Module-arduino-compatible-/111085883206?pt=LH_DefaultDomain_0&var=&hash=item19dd3c0f46

Michael