I had a Genie TZ50/30 for ~7 years.
The SD64 is an entirely different animal in the most outstanding of ways. It weighs 1klbs more than the trailer mounted version of that boom (TM64, without a jib), but the weight is across 4 ~15" wide tires instead of 2 trailer tires carrying 7klbs or so.
The travel speed is downright scary fast in tighter areas, but it's completely adjustable (pump swash plate angle via knob in basket) and the drive control is proportional (forward/reverse lever). Driving around a neighborhood will be a snap, which would be a great help after a storm. Drive from one job to the next at a very fast walk. Gradability is excellent, it's rated for 24*, but I haven't taken it to the tractive effort limits yet. It had no problem climbing onto my gooseneck flatbed.
The steering on the "front" axle is controlled by a rocker switch on the joystick, the rear axle is controlled by a rocker switch on the control panel. I could see the desire for the joystick to be 2 axis to allow steering the front axle with the joystick and the rocker being the rear axle, but it's not a big deal as best I can tell. The coordinated steering's inside turning radius is ~5.5', which is nuts. You have to remember to slow down the pump (knob control) when turning that sharp or it can be a bit tough to hang on in the basket.
The suspension is a nice touch, although a suspension lock would be nice to hold the suspension collapsed on the low side of the outrigger setup. That would allow you to set up on steeper areas and still be able to keep the tires off the ground. I'm guessing there's ~6-8" of suspension travel, although I haven't measured it.
The bottom boom is like an elevator on a 70' bucket, it travels straight up. This is awesome for a few reasons, but the main reason I liked it to start with is you have full reach from ground level until the bottom boom runs out of height, which is around 32' working height according to the chart.
After I talk to Nifty about becoming a dealer I'll make some videos showing the various features of the machines. Hopefully it'll be dry enough next weekend-the following week to start knocking some work out.