One downside I can see for this: it looks like, if the user had a seizure, it would be extremely dangerous. It would keep them in the seat but interpret their movements as erratic hard accelerations and sharp turns.
You're right. However, I suspect there are a lot of people who want this precisely because it's an electric wheelchair that's not been designed for the lowest common denominator.
Most of the electric wheelchairs seem to want their target market to be "all disabled people". This means you have to limit the speed, agility, control sensitivity, etc. so even people with (say) Cerebral Palsy can control them without putting them in danger.
There is a market for disabled people with full arm control and no proclivity for seizures who just want a fast, efficient way to get around. Right now I think the most popular way is to buy an electric wheelchair and mod it, but there's probably a market there for an off-the-shelf solution.
Independent of the answer I feel that this can also be applied with any human beings (with disabilities or not) and cars.
I don't think it's meant to be a one-size-fits-all wheelchair.