My experience is fairly consistent with LifeAquatic's. I was able to get good results as far as lower N and P with Chaetomorpha or a carbon source. The total amount that either can handle will vary, as you'll need stronger lighting and more space for Chaetomorpha, but if that is sufficient, it can do pretty well. I'd say with limited space and lighting, carbon dosing will easily outperform Chaetomorpha in terms of sheer uptake capacity.
Of course, I'm a bit biased, but turf scrubbers are also quite efficient--enough so to outcompete Chaetomorpha--but considering that my lighting is more limited, as well as space, the scrubber turned out to be a more effective option in my case. It is efficient enough for me that it eventually limits itself without a fair amount of food input--I have to actually add P in order to reduce N, otherwise there is a very slight rise in N.
I suppose what I really wanted to say in the end was that all of the above are fully capable of doing what you want them to do, depending on how each methods' needs, maintenance, and consequences are approached. Take the time and weigh those and decide whether or not they are right for you.
