Ive have used the MK3 long range deben and the B&F and i can say that the deben does its job but if you have it near electric power lines , mobile phones , Cameras basically anything with any kind of power supply then it is touch and go wheather you get a accurate location from it which i'm sure most people would agree is not a good feeling when your dog is to ground. As for the B&F it may have a fault but ive not come across it yet so my choice would be take that bit longer to save up and get the B&F i'm sure your terriers are worth it