Hi, Mini Kick is great! and will grow more with your child. the Radio Flyer has less turning mobility and is wider, so more stable for a very young child(about half the price of the mini kick, btw), so I suggest you choose between the two based on how coordinated your child. The scooters with two wheels in front are more stable than scooters with two in back and one in front.
The Radio Flyer is bulkier, so a bit more awkward to carry.
Scooters are a great urban way to transition kids out of strollers but still keep them moving when you are going places! a lot of fun!
Cheers,
C.