I bought a Zaon MRX from Transair and used it on a few trips around the London zone. It wasn't a success: the LEDs were flashing away at high speed due to the multiple contacts but the main problem was that without any 'bearing' information there was no steer on where to look. All it really told you was that there were lots of aircraft in the vicinity. It also kept your attention too much inside the cockpit when I believe you're much safer just looking out. .... so I took it back for a credit (which Transair were very good about!).
In practice I think these systems are only of value if you go for a more expensive panel mount version such as an Avidyne TAS600 (see
www.leesavionics.co.uk ). This is able to grade the threats as well as provide bearing. The principle advantage is that it then calls out over the intercom warnings such as "traffic 12 o'clock level and closing" etc, and so you can keep your scan outside the cockpit at all times which is the critical bit.
This of course requires everyone to have a transponder ... and to turn it on
