I've had a 6' about 8 years and it does a good job, I usually subsoil first. It's better if the soil is not too dry. Adjust the rear discharge to get the disired result.
I purchased the king kutter 5' professional for my L3301 last spring. It has been a tough tiller and I have tilled through a lot of rocks. The only problem I have with it is that it is green!
I also own a King Kutter 5" reverse rotation tiller. Very heavy duty and does a fabulous job breaking up the soil to very fine consistency. If tilling new area I cut all the foilage first then till in one direction then on the next pass till at 90 degrees from the previous pass.
I have a King Kutter (not sure if it's "professional" or not). It does a fine job and has never given me any problems but I've only had it for about 3 years? Use it once or twice a year. I did use a middle-buster the first year to rut things up first.