What is necessary is to make the sellers of various scooters etc much more accountable for who they sell to and what they sell them.
They are supposed to assess a buyers ability to control the scooter/power chair etc, and they are not supposed to sell someone something that they cannot control... however, many absolutely will sell your blind Grandma who can't relax her grip without a letter in writing and three months prior notice, a scooter that will do 8mph (scooters stop when you let go. Most peoples reaction in a panic is to grip harder!)
They should also make you aware of your liability should you cause an accident.
For my power chairs..
NHS: had to demonstrate I could use it indoors in a brief session (most of which was covered by my use of my manual chair anyway)...
3 months later I did an outdoor test which was every bit equivalent to a driving test - use a pedestrian crossing, navigate uneven pavement, reverse park, reverse around a cone, circle around a cone forward, cross a steep hill, go up a small kerb, alter the speed setting appropriately for where I was, do a ramp.
Was not allowed to use it outside before passing that assessment.
Private chair, reputable manufacturer (not dealer): Very similar but a rural environment, down hills, tracks, tree roots, field, gates, tight turns etc.
No one I know (and that is quite a lot of people!) who has bought a scooter from a dealer, has had to do more than show they know it goes forward if you squeeze/twist one way, and stops if you let go, and where the button is to flick it from tortoise to hare mode.
As for going on the roads with them - damn near every trip out I make, I end up going on the road when I have no desire to do so. Twice in the last month I've had to go around a small roundabout, because I've been forced off the pavement by some inconsiderate car user, and without a dropped kerb before the roundabout, have been unable to get back on!
It is incredibly dangerous, I haven't the speed to get out of anyones way, nor the height/size to be particularly visible.
However drivers should be aware of what they may encounter on the road, and class 3 mobility vehicles ARE road legal, and many non-road users have to interact with roads regardless of whether they want to or not!