Well, first off, when someone witnesses a guy engaging, with visible dots on the horizon, one assumes you have SA, before I ever engage, I always give a 360 look around for co-alt, or higher cons near me if I am to dive into a con. Now, OTOH,if you are on climb out, and cons appear anywhere behind your 9-3 clk, then a check six is valid.
Check six's are nice to have, but if you have to depend on them for your SA, then your SOL.