Your right the Origin B2 is more expensive but you are getting more for you money the Bel Target 550 will only detect Gatso's and laser albeit leaving it too late to do anything about. When I bought my 550 two years ago I paid £360 so they have reduced in price quite significantly but they are now up against some strong competition in the radar detection market place.
The Origin B2 also, via GPS, detects Truvelo and SPECS so as I suggest you are getting more complete protection.
As far as fitting is concerned I'm not an auto electrician and I fitted it in 30 minutes. The two sensors, GPS and Laser are plug in connectors and the power is taken of a cigarette lighter, once all plugged in I just tidied and tied the wires and shoved them behind the drivers foot well cover, it couldn't be easier. If you go the Origin B2 website you can download the manual.
I hope this helps and good luck convincing the Mrs!