Truthfully, Paul, even seeing one of these things advertised my very first thought was... "Oh, God, NOW what's happening to fly fishing?
And, thankfully, after doing more research on them, I STILL have that same opinion! They started out as "Golf Swing Analyzers" and, that right there, turned me against them! (One sport, that no matter HOW WELL explained to me, about its benefits, I still don't see the point in).
I, suppose, if one was so intent on having that "perfect casting motion", as golfers seem to be on "that perfect grip and swing", then maybe it'd be worth looking into!?! Or, perhaps, if one owned all the hi-end rods and reels, owned blue ribbon water rights, (with cabin), and maybe was bored enough to "want something new" in their arsenal.......why not, a new toy?
Even though I've often been accused of "making beer, instead of casting", when working some pools, I just don't like the idea, (for ME anyway), of "adding electronic gizmos" to a sport I enjoy, that I use to GET AWAY FROM such things, in every day life!
Actually, if anyone wants to improve their casting, the leather wrist strap system, that connects to your wrist and rod, seems to have helped an awful lot of people.