Hard to say as fx5 is a good name and well made, tried and tested,
However it works upto aquariums of 1500l so it's going to be working at its top end and any slightest reduction in flow rate may not clean your tank properly
Is there a fx6 that would be better?
Fx5 About £215
Pros

well made
Good name
Looks as good as it cost
Cons

expensive
Will be working at its top capability
1500l aquariums
X2 allpondsolutions 2000l/h about £140
Pros

cheap alternative
Combined upto 2000l aquariums
If one breaks down still have one working
Double the good bacteria

Cons

look cheap
Having 2x canisters and all that pipe work
Have to buy x2 media when replacing
Obviously there are more pros and cons to both but these are the basic thins to look at.
The fx6 on amazon cost £5 more than the fx5 and maintains aquariums upto 2130l. Is this an option?