What have you specifically checked? There are several places you could have a wiring problem that would cause failure. Did it ever work? How did you verify voltage on the blue lead to the towed vehicle control box? Did you 100% verified 12v, ground and brake lamp switch connections on the towing vehicle? On the control box end in the towed vehicle, did you check and verify that the blue lead (and all others for that matter) is actually plugged into the control box? Have you verified that the cable between the towed and towing vehicle is not the issue? Does the break-away switch activate the system?
I think the UTB is a great system. Even with a controller at $300 replacement cost if you actually need it, it's still cheaper than a complete new system from anybody else. Additionally, if you can find a qualified electronic technician, he may be able to repair what you have inexpensively.