From their website
"While riding over obstacles, try to go over them first with one wheel and then the other. Do not go fast. Be careful."
They aren't kidding about that. If you encounter an obstacle quickly that it cannot power over immediately, the rider is thrown forward which is interpreted as a request for maximum power. One wheel might jump over while the other spins in place resulting in a full power spin which can throw the rider out of the chair.
That is a key difference between a standard electric chair and any of the balancing Segway type vehicles. In a wheelchair, if you get stuck, you are just stuck, not injured, on the ground, and stuck. Standing ambulatory riders have a greater ability to quickly shift their weight and manage the inherently dynamic operation of these things.
If the batteries run down completely, it won't fall over because it has the kickstands, but how will you get anywhere with a dead battery? On a standard chair, you can disengage the motors and have someone push you. You cannot push kickstands.
Some conditions require specific seating positions, or the ability to change positions to avoid 'hot spots' on the skin which can become a real problem if the person has nerve damage and cannot feel it.
With that said, 2 wheels are a LOT more fun. If the person you get the chair for can handle it, they will much prefer the 2 wheeled vehicle.
But if they require a wheelchair, they should also have a real wheelchair. If a manual chair is not suitable, there are good power chairs on the used market. No used chair will be perfect because it was not made for them. As someone who uses a used rehab chair that doesn't quite fit, I know it can really be frustrating sometimes. But if the person has enough mobility to transfer without pain or too much difficulty, and someone willing to help with adjustments from time to time it can certainly be good enough. The type of chair I needed would have been over $30,000 new. Insurance probably would have paid 80%, but I found a good enough chair a few years old in like new condition except for trash batteries for $500, batteries were another $300, programmer is $500. It sucks that they lock users out of the controllers because equipment suppliers do a terrible job of programming usually, They charge $50-$100 every time they plug in the programmer for 30 seconds to tweak a setting. The best settings for a given operator are not known up front, they are learned over time. As the operator gains more confidence and understanding of the machine, delays should be reduced to 0 if the operater has good enough reflexes. DME companies treat everyone like a stroke victim and set all delays to maximum which makes the chair really hard to drive, and worse, really hard to stop. Given that you came to this forum, I recommend http://www.wheelchairdriver.com/
for good info for anyone that is really interested in going places in a wheelchair.