On a pass through, the FOB is pulled out of the arrow with the nock, and marks the point of impact.
I didn't see much difference with them, if the bow was tuned right, the steering gear didn't make a noticable difference for me. I didn't like the nock being pulled out, it tended to loosen the nock in the shaft over time.
You are somewhat limited on your arrow rest options, and need a large opening for a containment rest for the FOB to pass through.
