I think the improvement is slight but noticeable. I assume it increases the efficiency and ability to draw in air as needed. I've put about a 1000 miles on it. One thing I have noticed is that it seems to eliminate the effect of crosswinds cutting down the airflow.
It may just be a very small improvement, but I intend to keep my airbox and the bellmouth finishes it off. I like having the airbox and this makes it more like it should have been designed to begin with. It also comes with a stick on piece that goes behind the bellmouth (toward the rear wheel) that blocks any water that might get through. All in all, the cost of a UNI filter, removing the snorkels, and adding the bellmouth is not very expensive opposed to installing airbox alternatives and very simple to do. If someone did all three of those things at once, then they would go wow! that's an improvement.
I may try going up one size on the mains from 125 to 128 and see what it does to my top end. I would rather be under than over on the mains, but I was already on the edge and now might should go up one.
