I have two extenders - the old one that had 1xRTT data (at my summer house) and the new one that has 3G data for my house. Both are fine as long as you are within the range, which is generally a 15 to 30 foot radius (so long as you can see the device.) if there are walls or obstructions in the way then radius is more like 15 feet than 30 feet.
It works fine. When I'm in either place I have wifi anyway so I don't care about the data feature but it does work fine. You can tell you are using the extender because when you make or receive a call you hear a double tone just before the line rings (when calling) or when you answer the call.