If the FX5 has sensors i would like to know why it worked while the motor was removed? I dont think they have done anything but change where the water is pumped from( if the motor is in the top it's more likely to stop circulating from an air pocket) And add a simple timer to turn off every 24hrs, i dont think there is any fancy technology advancements as you put it.
And yes the canister was full when i plugged it in.
If you get a chance to look inside 1 of these beasts you will notice a breather on the inside of the lid, this allows any air within the unit to escape through the outlet. Because the motor is in the bottom its always submerged. The motor pushes the water up through a tube to witch the breather is attached, therefore sucking any air from the top of the unit out on its way back to the tank.
As far as the cost of filter media, i probably wont have to replace the bio balls that cost 10c each. There isn't as much room in the centre stack anyway for many bio balls or noodles as say a AQUA 1 CF1200. however the foam surface area is amazing. The replacement foam pads cost around $20 for 3 of the 6 that are in the unit. for 3 polishing pads it was about $15 AU.
I actually use the pot scrubbers in my small in tank power head canisters. they are alot cheaper!