check6 button is
almost worthless compared to range vox calling a con when hes starting his dive 5k out, or even just calling inbound badguys when your busy.
if I get a check I always reply even if Ive seen him. that way friendlies get an idea of how good your SA is. I always thank the friendly if its a good check*, that way he might save your life the next time
people really do appreciate decent comms, and it counts for
alot in a furball. nothing more annoying than flying in total radio silence when you can tell easily by the way theyre flying that the enemy are talking to each other.

* by good check I mean timely and
describing the threat, or if its very late just what to do about it. anywhere from info: "headsup xxxx, coupla 190s inbound 15k ish" so the friendly can build his SA picture and decide what to do about it, to instruction when the friendly doesnt have time: "xxxx six! break! break!"