I have the Makita sharpener so my chisels are flat ground. My new Barr chisels came with a hollow grind, which seems to work just as well, I can't say that I have noticed a difference between the two styles. When the Barr's need to be reground, it will be done on the Makita wheel (flat) because I happen to have one.
I have however noticed a difference in the angle of the grind. Lower angle (25 deg.)works much better in softwood than 30 deg, which holds up better in hardwoods. I have an old laminated chisel (Ohio Tool)that was ground at about 20 deg when I got it, and had big chips in the edge. It chiped easily when I resharpened it until I changed the angle to about 30 deg. Now it holds up fine. Tom