So like most things, there is a downside, too. The HST is great as mentioned above but a downside is that at one point I was in a sticky place, wanted to hit the right brake and do a power turn. With a gear tractor, it is standard practice. With HST, you need to hold the trottle with your left foot and use your right foot for the power braking. It works.
I am so pleased with the power to PTO ratio. I mowed with the five foot brush hog through thick field grass, first cutting and it just chugged along...almost as good....almost as fast as our 40 hp gear with that same five foot brush hog. I had to wonder how 21 HP can deliver so much?