Dave writes:

Just to throw in .02 re your TCAS comment..................

We have the ZAON XRX on board our Cherokee in a VERY busy environment
(100,000 operations /yr)

I cannot begin to tell you how useful this tool is in tracking
trafffic around us

For $1500 !

The Sandel ST3400 is a TAWS/RMI display that also includes TCAS capability,
with a fancy back-projected LCD display. That's probably why it is so
expensive. I suppose TCAS alone is a lot cheaper.

I looked at the ZAON XRX on their Web site and it looks like a pretty
practical gadget.