We had Ooma before we went on the road and it was just fabulous. Excellent call quality and, at the time, completely free after buying the box. I still sometimes use it in parks with good Wifi but poor cell signal. I fully intend to put it right back into service when we're off the road for good.
The bluetooth adapter seems to allow you to use your cell phone through the Ooma box. Can't imagine why you'd need that. And Bluetooth has a range of about 30 feet, and not through walls.
If you have good upload speed on your internet connection (100 mb or more) I think you'll love it. You can even hook it up so that every phone in your house, wherever it's plugged in, will work through Ooma's connection.