I have flown with TAS 600 series TAS on a variety of platforms with a variety of displays. I've some perform as per the manual and some perform terribly (180 Deg out, terrible range etc).
one thing that we found was that there are 2 levels of test in the manual. the primary test gave false serviceable results but the deeper test found hidden faults (primarily with the LRU) that manifested to the pilot as poor bearing resolution.
Once resolved we've had some good service out of the TAS linked to various polar or map displays. I agree that a map background is best so you can relate the range to ground features. Unfortunately we have some airframes fitted with a text based 1/2 ATI display which is diabolically awful. We also have some Neanderthal aircrew who insist that avionics are the devil's work and pilots must not look at them (hence the text displays when polar ones were available). I believe there is even one airframe where the handling pilot has to turn off his screen so he cannot look at it (the co-pilot has one too fortunately).