Footlock is more direct--one foot of rope pulled means one foot higher. Body thrust cuts the force needed in half, but doubles the length of rope (pull one foot, go up half a foot). It's really about preferences here. I prefer footlock--I get there faster, then have a minute to catch my breath while I tie in.
Spurs should only be used for removals or emergency rescues (and rarely even then). They injure the tree and expose it to problems that can lead to failure years down the road.
I always footlock up big trees! Both for prunings and removals.
It is a nightmare to spike your way up a big stem.
And the more you footlock, the better you get at footlocking.
i avoid body thrusting like the plague, footlocking is faster and you use less energy getting into the canopy. SRT is a technique i have been exploring as of late, and see the advantages of it. And yes, spikes can NOT be used to prune, removal/ rescue only!