Does anyone else have experience of how well the units work?
On the point of it not providing bearing info - I would hope that if a unit told you that there was traffic nearby then you would find it visually, regardless of what info it gave - and that range and altitude would be sufficient for this. If it is out of line of sight behind the aircraft, then odds on it won't be a threat in most cases, at it will either see you ahead, or have insufficient speed to catch up.
I have seen euipment on sale for installing in a panel and hooking up to the electrical supply for the 300-pound set.
In the case of the two Tutors yesterday, they would very probably have been in range of a ground station interrogating their transponders, and therefore the equipment would probably have prevented this tragic accident from happening.