The optimal filtration volume is at least 10% of water.
So if you have 100L aquarium the optimal is 10L filter...
I have Tetratec EX 1200, (12L of filtration volume) and its not enauf for my 180L of water. I wil put another filter (ex 700- 7L of filtration volume) so I will have 19L- optimal.
A filter is not good if it has a lot of flow but how it filters and U4 like i saw till now its not good. If you wonna have a good filter try to find Fluval 4plus... They dont do them anymore, but its the best internal I ever had! True story
I had an 3plus for my 100L aquarium and was awsame!