I remember these first starting to hit the headlines here around twenty years ago when I was regularly pole fishing the Trent for Roach, wasn't the standard shotting pattern to overshot, laying on the bottom, so that when a fish picks up the bait it lifts the excess shot and sinks the float to indicate the bite?
I'm not saying they don't have their day but I've never really seen the point, ok you might get away with a lighter float but I generally tend to go as heavy as the conditions dictate with a 'conventional' float and it does the trick.
Flat floats just appear to be a variant of 'laying on', possibly brought over from the continent as their standard take on the theme.
But the grass is always greener, as they say, especially the tackle dealers.
I can't really see the bait acting any differently and given that that sorts the presentation there are plenty of other floats which will do the same job... Namely registering the bite.
Over complicated and unnecessary imo, but I'm probably wrong lol