Rancar,
The reply from "rubintrophen" was pretty good, but (ain't there always a but?), there is more to the story.
The engineering of a Woods, JD, or Landpride is going to be a cut above KK or Howse. Some may doubt it, but think about this, my Woods Brush bull 600 cutter was engineered to allow the blades to be changed with hand tools. I did mine after a season in about 30 min, including jacking it up. And I only used one hand wrench, 5/8th if memory serves. KK (and others) require a LOT of torque that only a top of the line 1/2 impact or 3/4 impact wrench can provide. My neighbor sells blades and for KK he almost allways sells new bolts/nuts with the blades as they typically are torched off. The highway departments that have the BB go 3 sets of blades per set of attaching hardware .
Want more? Measure the size (diameter, thickness and weight) of the stump jumpers on a Brush Bull and a KK or Howse. My 60" BB has about 2x the diameter of my buddies 72" KK. He gets stuck on stumps with some reguarity, I have not gotten stuck (yet). He also grabs a pocket full of shear bolts every time he goes out, the BB has a slip clutch. You can get a slip clutch on KK, but it raises the price and quites the bang you get for your buck. A larger stump jumper also means shorter blades. Because stiffness goes up with the square of length, a short blade is much much less likley to bend when you whack a solid object.
Now for reality, the BB 600 medium duty it about 50% more than the KK medium duty unit. And it is about 3x the price of the KK light duty kutter. Is it "worth it"? For me, yes. If you only use your's casually, on smaller material, the KK may last a lifetime. They are good solid units, but they don't have all the bells and whistles, not to mention paint and weld quality you will find on a JD MX or LP 25xx or Woods BB series.
Like my daddy used to say, "You only buy the best once".
Best of luck,
John Bud