the cape is nice for druids who like to try to PvP in the skies.
But, you need to have the cape on hotbar - it has to be 'clicked'/used.
Annnd - it only works for 10? 15 second?
So, if you click it TOO soon, you will slow fall. Then, resume fast fall. and still die
Nagrand is a GREAT place to 'practice' falling. and aerial PvP
If you are feral, you can also target someone on the ground and feral charge, which 'interrupts' the fast-fall.