The Nutrafin systems are a bit of a waste of money, I have 2 of them. The canisters are too small to produce a decent amount of CO2, and the bubble ladders get blocked really easily which causes the bubbles to just dash for the surface.
These days I use DIY, with the outlet passed through a venturi on a small water pump mounted low down in my tank. This produces tiny bubbles constantly which spend quite a long time swirling around in the water column because of the current from the pump and also from the outlet of my external filter.
I did vary from the usual DIY instructions slightly, I used 2 litre pop bottles instead of 1 litre ones, and doubled the incredients. This way it produces a lot more CO2 and works better for my 180l tank.
Oh and in answer to the original question, in my opinion any CO2 is better than none at all.
Ade