Ket,
I have a 56" Yanmar tiller that came with a 2010D. Over the past week I tilled for about 4 hours on the tractor's hour meter. During this time, I developed a new respect for these Japanese tillers. I tilled the first pass at 540 RPM and the subsequent passes in a higher speeds until finally tilling in the highest speed which is well over 1000 RPM. I made a total of five passes until the field had no dirt clods bigger than a marble. I don't think that anything but one of these tillers combined with tractor capable of multiple PTO speeds could have done the job as quickly.
These tillers allow for higher tilling speeds that US tillers at a fraction of the price of a new US tiller.
However, they do not appear to be constructed as heavy as some domestic tillers. For this reason, I am very careful when tilling around roots and areas with rocks.
The wheels at the rear of the tiller function as a depth gauge. They are used by setting the depth with the 3 point hitch, and then adjusting the wheels to maintain this depth. When the wheels are set, then the hitch can be lowered all of the way down and regardless of bumps or holes, the tiller stays at the given depth.
In short, the Japanese use their tractors mostly for tilling and they have perfected the tractor/tiller combination. There is nothing in the USA that can compare to their features. If you can get a Japanese tiller in good condition and at a fair price, it may be one of the best values out there.