The handlebars are probably a bit too high. The scooter itself is quite long.
We have this scooter and a Micro with smaller wheels (~100mm). Our daughter prefers the Micro.
The Hudora Big Wheel Air 205 is sturdy, but would not recommend it. The wheels are impractical, have to be inflated hard so that the power is converted into propulsion and not absorbed by the wheels. I subsequently got solid rubber wheels.
I find the Hudora Big Wheel a bit long (impractical for the boot and public transport) and the footboard too high (forces a strong up-down movement when scooting). Would rather recommend the Micro - also with 205mm wheels.

I don't think so. I use it as an adult. A teenager can also use it well, but a child of 4 definitely not.

The product is indicated for ages 6 and up. It is a robust scooter with some weight, which is why I wouldn't necessarily recommend it for children aged 4. It also depends a little on how big and strong the child is.