Sorry to dig up this old thread but I am in exactly the same position as Practical Fish Magazine are doing the same offer where you can chose either the U2 or U3 free as a free gift.
I too currently have the Juwel Internal filter in my Juwel Vision 180 but for the last 7 months or so I'm also running an external JBL E900.
My query is about the heater.
The heater in the Juwel internal sits inside the canister in its own storage compartment. Does the Fluval or if swapping would I need to buy a heater to attach to the tank wall?