P.S. I have syndrome shuttle in my U5020C and I have no issues with it and am not sure I would want HST if it were available. Power shuttle? I think I would have liked that option, but not worried about it at all.
I've finally got some serious time on a power shuttle, and I think it's pretty darned nice, but there are times when it's definitely not as good/handy as HST.
I have an area that I'm adding fill to and it's pretty narrow...imagine a raised railroad bed. I'm widening it in one spot to put an 8x8' shooting backstop (widening so I can still drive past it). I drive down the lane, and turn to the left to dump the fill in the new spot. I then back up, with the wheel to the right, to start a u-turn. That puts the machine perpendicular to the lane, and I have to back up close to the edge (3ft vertical drop off). That leaves me steering while looking over my shoulder. To keep my left hand near the shuttle lever, I have to steer with my left hand and look over my right shoulder, which is sort of awkward, but you can't really steer with your left hand and look over your left shoulder. I have to take my hand off the wheel to flip the shuttle lever to F, and hit the brakes at the same time so I don't go over the edge. If I miss the shuttle, I'm fighting the engine with the brakes, and I could see how easy it would be to have your foot slip and over the edge you go....bad day. Even if you don't miss the shuttle lever, you could have enough momentum from backing up that missing the brake pedal would have you go over the edge.
With an HST setup using two foot pedals, all you do is take your foot off one pedal, and push on the other pedal....pretty hard to miss, and the HST stops pretty much as soon as you let off the pedal, so it's less likely to wind up going too far and flipping the machine.
I really do like the power shuttle, but I recognize it has some limitations (they all do).
