I have now used both the Billy Goat Outback and the DR Field and Brush Mower and can compare the two. I have a little over an acre that I just purchased and it was covered with cactus, mesquite trees and every kind of thorny bush known to man. It is also very rocky. I rented a Billy Goat and cleared the first half. The Billy Goat did a pretty amazing job, but there were a lot of the mesquite that I had to cut down with a chainsaw. The Billy Goat would try, but it was a no go. The narrow tires and lack of differential lock got me stuck a few times.
The DR is a monster. I purchased the 30" with the 17hp Kawasaki and it never broke a sweat. I only had a couple of mesquite that it wouldn't handle and the wider tires and locking differential prevented me from getting stuck. The DR is heavier than the Billy Goat, which is good and bad. The DR is harder to turn, but the extra weight allows it to bend over more brush. The gearshift on the Billy Goat is down by the engine and you have to bend over to get to it. Sometimes, that area is obstructed by thorny branches. The DR shift lever is up by the other controls. The shift on both of them could be smoother to operate. The only thing I really missed on the Billy Goat were the handguards. You have to keep your left hand on the presence lever or it will stall if the blade is engaged. If you are in a bunch of thorns, you will get scratched.
Sure, I could have continued to rent the Billy Goat and come out money ahead. But now I can go mow on a whim, don't have to reserve the Billy Goat and don't have to return it to the rental yard early Monday. Convenience is worth a lot.
I am 64 and mowed most of the day Friday. In most cases the DR is no more work than any walk behind mower. I don't understand the comments I have read saying that it will really beat you up. So far I am very happy with the DR.
Barry