New Holland T2310 (40hp), Kubota L3010 GST, New Holland TC21DA *** Previously - Farmall H, 1941 John Deere B, Shibaura SD1500, John Deere 850, Bobcat 642, New Holland 1925
Can't speak to the heavy duty model, but I have owned a standard duty 4' and 5'. I cut 8' tall brush with a 15hp Shibaura. It made quite a racket, but produced nice trails. They run nice and smooth.
I have a 6' that I use behind my L3010. I bought it used and am very pleased with it for what the investment is. Mine has the 60hp gear box & shear bolt. Once I figured out how to operate it the shear bolt has not been an issue. I paid less than 1/2 price of new for it & feel it has been a great value for us.