Really, the only way to go. No matter how fast you can tie a knot, you cant beat the speed of opening the gate. Plus alot situations call for the needed weight to toss out a biner for balance point rigging. I only use slings for lowering several branches at time, slings are a lot slower to undo then a biner. Plus knots really seem to rattle goundys.
I can see the sling deal for lowering multiple branches at a time - on a conifer. admittedly tying three of four cloves at a time is slow to tie and untie. As far as this biner deal goes with the hardwoods, maybe you need to take fewer (bigger) cuts, and make them count more.. just thinking out loud here.
Funny how some the newer guys seem to think people haven't been taking down bad ass trees sinse long before they came along (myself included). Some of the techniques I use on really tricky (and or big) trees, I know have been around for at least 30 years. But what do I know..