I never complain about check 6's why because it's my responsability to check my own. Reaper makes a good point about if you get shot down and theirs a friendly on the con that shot you down, it'd be nice to have in those cases. 99% of the time when I get shot down I know they are there. Rule of thumbs I use are:
1. When in an harsh environment update SA min. every 5 sec. that means looking up,left,right,back and underneath.
2. When behind an eny plane don't get to focused on him he can't shoot you down at this time, work for position but you should always check rear, left high and right high for pickers.
3. If eny plane starts to climb or turn immediately check your views while pulling up or turning at the same time. This can be done in .5 sec and it will save a lot of deaths if you do.
That's what I do anyways