I have one and use it mainly when testing equipment changes,
I feed the arrow speeds and mass into software that gives me ballistic data, sight marks etc.
I have also used it to compare minor form changes, ( e.g. a deeper grip on my third finger gives me a more consistent but slightly lower arrow speed ).
I also sometimes just try and shoot arrows with a consistent speed, as a variation on blank boss practice.
but at the end of day it's really just a toy.
