They are meant to ease the breakover of the foot as the front of the shoe is set further back behind the toe, hence horse less likely to trip, more like a natural foot shape (here horse would naturally roll the toes down from walking on various surfaces). Personally I am not really a fan, went to a farrier once who was very pro-natural balance, put some on my horse and he was lame shortly after I am sure they work for some horses but I would rather take the shoes off and let the foot do it's job itself, but I'm not very keen on horseshoes anyway so am quite biased!
Local [world class] farrier makes a nice income from these, I had them put on my boy [who has perfect feet], by this world class farrier, he was "walking on his toes", entirely unbalanced, I had them off and later went barefoot.
Part of the argument is that over a lifetime the horse will wear a metre of steel off his toes, well thats not a good thing, but somehow mother nature has worked something out, and my boy has lovely toes! Better frog, sole and digital cushions too.
I tend to find that transitioning a horse out of NB is more challenging than regular shoes - because the hooves generally have more contracted heels. Doesn't mean it can't be done, just extra care needs to be taken.
One of mine is in natural balance. He came with them & I'm a believer 'if it's not broke....'
He does have crap TB feet but [touches everything wood wildly] is sound & sure footed. In fact This shoeing + micronsed linseed seems to be improving his feet brilliantly
My pony has had some ongoing mild lameness. Vet did x-rays and nerve blocks at the start of this week and he reckons it's a hoof balance issue, so we're working to correct it gradually. The farrier came today and did a little trim, also fitted NB shoes...