You don't need one, no.
But, a hob or canister filter does provide mechanical filtration (removing debris), and also gives you a way to run chemical filtration (activated carbon or chemiclean for example)
So although its not needed, it does provide benefits.
Personally I would suggest a hob filter is better. A canister filter will trap debris and food particles in the canister, which will need to be cleaned very frequently, or the food particles will break down and elevate the nitrate. Removing and cleaning a canister is a pain. HOB is very simple to dissassemble and clean and reinstall.