I think the niche of "personal vehicle that you can take on the metro" is better filled by PEVs. Shrinking down a bike's drivetrain size is harder than just putting together a single wheel, some circuit boards, batteries, and an electric motor to make an electric unicycle.
A big advantage EUCs have is you don't have to bother with folding like a bike, just hop off, grab the trolley handle and walk on.
Electric scooters have similar advantages but they have to compromise range, performance, and compactness for their ease of learning.
I haven't had a chance to try a single-wheel electric vehicle as they are not street legal in Germany. But usually I vastly prefer riding a bike over an electric stand-up scooter. My weight is distributed much better on a bike, making the right more stable. On a scooter I cannot reliably raise one arm to give a turn signal. Not signaling can be quite dangerous on shared roads or narrow paths. I never see anybody else indicate their turns on these scooters, so it's probably not a personal problem. Did any manufacturer figure out a way to put easy to read indicator lights on these?
The other thing is that you actually get some light exercise on a bike. Most people with desk jobs would do well to move their bodies a bit more during their days.
One thing that's nice some times about scooters is being able to stand up tall, rather than get into a slightly hunched up position on a bike. The Kwiggle from the GP allows for quite a unique upright body position. So that may be intriguing.
A big advantage EUCs have is you don't have to bother with folding like a bike, just hop off, grab the trolley handle and walk on.
Electric scooters have similar advantages but they have to compromise range, performance, and compactness for their ease of learning.