Definitely worth the money.
We got a cheaper one, tenner, DD loved it. Tried a friends Mini Micro to see the difference & it is quite significant. The wheels are made of a spongier rubber substance, so they have more give in them and are more hard wearing.
There is a lot more suspension on the wheels.
The board you stand on is more flexible, so it has more 'give'.
Not only do these give a comfier ride, but it also means when you hit something - sticking up flag stone, brancg, stone etc - there is less chance of going flying off. DD has to hit something significantly bigger on her MM than the cheaper one, before she falls off.
The brake is also a lot more responsive.
The steering is more sensitive.
At first glance there may not look like £45 difference, but a short ride on both and you quickly know which one you'd rather have your child using.
Replacement parts / parts to customise your scooter are easily available for the MM too.
Good resale value too 