I've had a lot of FX5's and FX6's in the past and they usually last me 2-3 years and then something goes wrong and not having a back up it usually means buying another, repairing the original and selling it on. By comparison I've had an Oase Biomaster 250 for 4 years.
I've currently got a FX4 on a 300 litre and its going well so far, it is second hand but all working ok for 8-9 months I'd guess now. On my other tanks I have an Oase Filtosmart Thermo 100, Oase Biomaster Thermo 250 and an Oase Biomaster Thermo 850.
The Oase ones are my favourite by far, so easy to set up and run, they use standard hose's rather than the ribbed ones so you can use lily pipes, the pre filter sponges are so easy to clean its stupid not to. Where as with the FXs you always get a little bit of water trapped between the pipe clips and the valve when you disconnect and then you have to lug it out and strip it down just to clean the sponges where as with the Oase its just unplug, undo two switches pull out the prefilter and you're off. Even when you do the deep clean on the Oase it has a handle on the top so its super easy to move around, where as with the FXs you always end up clinging on for dear life and doing a distinctive waddle (FX owners know what I mean).
I've not had Ehiem before so I can't comment but would definitely recommend the Oase Biomasters as a solid investment.
Wills