Just picked up a Mott sharpener for flail blades- I had just read about how they are hard to find, searched, and found one on Ebay. $58 with shipping, seemed pretty reasonable.
The fields are horse pastures, so I'm not looking to make a golf green, that's for sure. We do have a lot of rocks, and sometimes I don't miss them all. I figured the sharpener might help when I bung up a few of the blades. I may decide it's easier to do it with the angle grinder, but it seemed like a neat little tool.