Bonnets load up way to fast. When the product is caked on. It's like polishing with a layer of glue. You'll spend too much time trying to clean it out.
Also, Bonnets don't have a nice smooth conforming surface which spreads evenly like foam does. Besides many products today use the heat generated by the foams friction agasint the surface to do most work. Bonnets use the same principle as wool which cuts with the nap. This makes it more prone to buffer swirl, trail, or holograms.
The only good use I've found with bonnets is wiping dried hazed product off. It simulates manually toweling off hazed product, especially when the dried product is stubborn. In most cases though, I find that it's easier to do this task by hand.