mcmxii how did you go about cleaning up the edges?
I rotate the cutting head 90 degrees so that it's vertical, then use a 4-1/2" angle grinder with an abrasive disc to dress up the cutting edges. The drum is very easy to rotate and it takes all of 5 minutes to clean up the 24 hammer blades.
If a hammer is in bad enough shape, I run a bead of 7018 along the cutting edge and grind it to shape. Here's one that I fixed up after a "friend" borrowed the flail. The last photo shows the final shaping stage, and come to think of it, I would have to look closely at the hammers to figure out which ones have been repaired.
After looking for hammers on line and seeing that they're expensive, I designed (in SolidWorks) what I hoped would be a cheaper and better hammer with the idea that I could sell them. But with steel prices being what they are I decided that they'd be no money in it.
If there's a downside to a flail over a rotary cutter it might be the cost of the blades. The cheapest I've found online are $21 each so around $500 for 24 of them. Of course, there's no need to change all 24 at once and I'll continue to weld and shape as necessary which is pennies on the dollar. To avoid any balancing issues, it's not hard to weigh a known good hammer and add/remove material to get the weight right on a repaired one.