We've found that the rotary rakes don't add rocks and sticks into the windrows as well as the older style rakes with the reels that tend to rope the hay.
We learned this from haylage as the chopper knives don't seem to hold an edge as well with the steady injestion of rocks and stuff found in fields.
I have heard the same. I am not sure I can justify the expense of a rotary rake. My rock situation is steadily getting better as the turf improves.
I am using a ground driven wheel rake.
D.