There is huge potential for standing HPVs, particularly in traffic, where the improved visibility is a huge advantage. After riding a Trikke T12 for several years, I was ready to upgrade to something faster, but was not interested in seated transport, as drivers treat cyclists like dirt.
I chose the StreetStrider over the ElliptiGO or 3G Stepper. It's a lot faster than the ElliptiGO, less expensive, and allows the rider to use arm power in a very natural combination with the legs. The SS is big and smooth-riding as well, over-engineered to the point that it feels like a little car on the road. That said it is very nimble and efficient. I ride one to work each day through the middle of Houston in rush hour, 7 miles each way. It is far better adapted to this task than my T12 or 26" mountain bike. The only drawback is that I can't take it on the bus.
Re: “Outdoor elliptical bike?”
I live in Houston, where roads are very flat, so I have no experience with crests. I can see where that would be very annoying on a strider. We have steep grades on overpasses, though, and I have no problem going up in low gear. I ride at least 14 miles a day, and have not experienced hot spots unless I wear the wrong type of shoes.
My assessment of speed came from the Elliptigo website. I have since learned that it is not as slow as they say. Both vehicles can pace a mountain bike, cruising at 15-18 mph with sprints up to 28 mph. I find that the strider is much more comfortable than a bicycle, with less fatigue. I attribute this not only to being upright, but also being able to use my arms. I love using my whole body for propulsion, and that is one area where striders and trikkes will always offer something that the Elliptigo cannot.
I also like the strider's size and inertia. While I wouldn't want the extra weight in Colorado, it is very well suited for inner-city rush hour traffic in Houston. My strider is my primary vehicle, so the stability of its three-wheeled stance is very important, since I have to frequently ride through heavy rain storms. It can also carry a lot of cargo, making shopping trips easier.