Gearman,
I'm using hammers on mine. I've cut just about everything up to about 1.5 inch diameter brush/trees, heavy vegetation, tall and regular grass without any issue. I have some swampy areas to maintain and since the flail mower is lighter than a brush hog, it works for me.
If you get into very tall/thick grass, you have to slow down a bit or take two passes. In some cases, I lift the mower up maybe 6 inches for the first pass, then drop it down for the second pass.
I like the mower. It serves my needs for occasional use and does a really good job. Just know that flail mowers don't work all that well when mowing in reverse. So, in some cases you have to lift the mower, back into an area, then drop the mower down and mow going forward.
The unit I picked up from Betstco was a very lightly used demo unit. She told me that they used it for one of their commercials. It looked brand new when I received it. I think I paid 1K for it, regularly 1.4K. Free shipping included.