What do you guy think about fluidized sand bed filters?

I just got a pair from my brother for Christmas. This is what they are:

Rainbow FB300 Lifeguard Fluidized Bed Filter.

They are meant for up to a 300g aquarium and they are going to be used in a 60g Reef tank and a 30g FW Planted Discus tank.

These are supposed to be no-maintenance filters.

Comments, good and bad please.