I've used slo-mo footage with phones and it sure is really good in seeing how the arrows do. And its so fast. Take a new bow, shoot bunch of arrows through it and film all. Then pick the one that flies best, easy.
I haven't tried it with flight shooting gear yet, but i'm looking forward to it.
The angle i think is best is of course straight behind the archer aligned with the arrow. There you can immediately see if the nock goes left or right.