My 2 cents on the 12 inch Champion Brush Blender. I am ENTHUSIASTIC about it. It is the only thing I have been using for mowing several acres (yeah I really need to get a mower when my ground is leveled better. I have lots of mole hills and grooves from black mud, and cleared of debris better) of tough grasses, some blackberries, etc. I have used 2 and 3 point flat blades, heavy trimmer line (.158 Oregon Flexiblade in an Oregon Magnum trimmer head), and circular steel blades and carbide tipped circular blades. The Champion is what I use for everything now.
Trimmer line gets hooked on things too often and breaks. The 2 and 3 point flat blades do not cut well unless they are at the proper angle to the material you're cutting. But the Champion blade works well because of the bend on the ends which catch the branches as it spins. I use it first thing when opening up an area. Let's say there's a lot of debris, I will cut the blackberries and tall grass and poison oak/sumac/ ivy, or whatever it is, so I can see what I'm doing to pick and rake up the branches etc. Then finally skim over the area with the Champion blade to mulch and mow what is left.
Or for an area that is heavy in black berries, I'm swinging the Champion blade sideways and up and down, whichever way engages the blackberry growth the best. Coming down on the vertical blackberry stalks, it chops them up and spits them out like a Salad Shooter.
Cruising over a smooth grassy surface that is not too dense, it leaves a close cut.
Where the grass is tall, I may hold the blade at a 40 degree angle or so, to get better mulching action.
The stock guard that came with my trimmer, recently got destroyed when the Champion blade hit a good rock and deflected upward and cut the guard 2/3 through, destroying it. So I cut the rest of it off. But even before that, the guard was not doing an adequate job of protecting me from the Champion blade that extends below the guard- I was still getting chunks hitting my lower leg, thigh, torso, right upper arm, hands. I got some bruises on my legs. And that guard tended to get in the way when I'm maneuvering around things. Now it never really gets clogged with grass- stuff spins free. I made a bracket and hose- clamped it to the shaft, with an arm that extends to the left with some heavy fabric hanging down from it- it catches a lot of stuff coming my direction. It is short enough to not possibly reach the blade. So at present, my protection is goggles under a Husqvarna foresters helmet with mesh, and gloves and heavy shirt. Chainsaw chaps would help the legs.
I started running blades on my 24cc Honda 4 cycle trimmer, but it died with low compression and it would get bogged down with the Champion blade anyhow. I have had the 42.7 cc Echo SRM 410U for 5+ years now, it has been great. Hit rocks and wood too often, but it keeps on ticking. I have to slow down some when mulching heavy grass, but not unreasonably so, considering it's what I can afford.
Sharpen the outside of the Champion blade a few licks with a 4" grinder, including the wings. The outside is sharpened instead of the inside as originally, so when I lightly go against tree bark, it does not cause so much damage. (The newer blades are sharpened on the outside). I don't try to completely grind out the rock dents on the edge- that would take off too much metal- just enough to put a sharp edge.