Hi,
im currently running a tetratec ex1200 on my 300l. I have the spraybar at one end which creates good circulation around the tank (you can see this if you watch small particles floating around). However, i also have a nano 600lph powerhead at the opposite end shooting towards the gravel to help circulation and you can definitely notice the improvement.
Obviously my experience is with a 50% bigger tank but tbh an extra pump is only £35 or so and would produce similar flow without the cost (and maintenance) of another filter.
However, it is entirely personal preference and people like to have an extra filter running in case something goes wrong.
Theres my ramble over with..Hope it helped
Howard