Everything helps
As mentioned in ‘another place’ where the same question was posed, I use the small Zaon unit. With all its limitations, it is better than nothing. I fly a relatively slow aircraft (the sort that gets bird strikes on the trailing edge of the wings), most other traffic overtakes me, so there is even less chance of me seeing them, although I hope they see me. When my unit starts to display, it reminds me to increase my look out. When it starts to beep too much, say in the circuit, I mute it.
I suspect the answer to the original question is that anything that helps awareness of other traffic is good. It’s a case of Mk1 Eyeball + LARS etc. + TCAS or cheaper equivalent + FLARM all the things that you can afford, power and use without too much distraction from the job in hand. My 2.5p’s worth (old money).
Safe Flying,
Richard W.