The only difference, Tora, is that the hire versions have a maximum speed of 12.5mph, the hirer must hold a full or provisional driving licence and be over 18. They must also complete an online "safety course" before their first hire.
The most significant similarity with the privately owned (illegal) versions is that if a pedestrian is hit by one with an adult riding it at three or four times walking pace, the outcome will be much the same.
My local Plod has thankfully begun to seize the illegally used versions when the opportunity arises. The miscreants lose their scooter and are also hit with a £300 fixed penalty and six points (for no insurance). A "New Driver" (that is, one who passed his test less than two years previously) will have his driving licence revoked as a result of this and will have to take his test (both parts) again. Many of them are blissfully unaware of this (as my local rag testifies).They cannot recover their machine from the pound as to do so will require proof of insurance and scooters are uninsurable against Third Party Risks.