Old people give up their mobility way too fast, often because of depression, isolation, or sheer lack of anything to do. A device like this will only accelerate the process. Young or old, we all tend to perceive a certain level of exertion as unpleasant, even dangerous, and that level is well below the level of exertion required to keep us fit and healthy. Obviously we are very poorly adapted to living in an environment where physical exertion is optional. The more we make exertion optional, the faster our bodies will degenerate.

I'd rather keep my legs working - those look very prone to ankle/knee levering injuries.

Does it look like a device convenient to use for an elder or someone disabled?

It looks like it may be difficult to mount & balance yourself on this if your mobility is limited.

See the few seconds starting at 1:13 in the video.

Many elderly suffer from amyotrophia, I doubt this being usefull device, except for people which are disabled.

While Honda, Toyota, and many companies in the Japanese robotics space do devote quite a lot of resources to thinking about the elderly population, a significant amount of the R&D work done is not done with the intent of being immediately productizable, but rather to do basic R&D and to fly the company flag. (See Asimo or, indeed, any robot which looks remotely like a human. Or the gigantic eight-legged spider robot who existed to wave a large fan at people that my tech incubator made, which existed to say "Look at us, we're capable of making a gigantic semi-autonomous eight legged robot with one functional limb which you could mount all sorts of things that are not cooling devices on.")