My theory for what it's worth...
When I started slow trolling with double hook rigs, I considered this hook. But the more I thought about it, the more I didn't think it would work. Reason why is, if you're slow trolling, odds are you are moving. And if you're moving, you're coming into fish every so often. And unless it's a bad day and you're putting it right in his face real slow, and the fish nips the bait, more times than not, the chance of hook-up is much less than with a leader of at least a couple inches. Otherwise they're gonna come up, or from either side, open that mouth, flare them gills, and get done with business right now. In my opinion, the difference between this hook and a hook on a leader is......I think the chance of a miss is great if the strike is hard because the main line is interfering with taking it in.....mouth open wide, line hits the lips and bounces off, pushing the hook back out before it has a chance to shut, or, reflex is quick enough to open back up when the line touches it's lips. I can see the problem even worse if the fish hits it from the side ......
Otherwise, if a hook/minnow is on a leader several inches long, there's enough slack there to let the fish ingest and hook itself, without the dead giveaway of the vertical line. That's just my therory, but it's what I believe...
If I Ain't Crappie Fishin', I'm Thinkin' About It............