Conan thier is no reason to be afraid of it. Its simply just another filter for our tank. As long as you know what its limitations are you can deal with it or decide not to.
Timbo, refugium with macro algae, mangrove patch, sea grass bed all pretty much do the same thing as each other just in slightly different ways. I dont think Thier would be a need to set up 2 redundant systems, but you could if you wanted. ALgae will remove nutrients from your water system, but as with everything they have thier limitations and good things. Maybe I can shed a little light.
With the use of Algaes we all have to be mindful of the plants going sexual and/or releasing the toxins back in the tank. And we have to watch for the algae/calurpa also taking over the tank (been their done that). Let me see if I can shed a little light on the methods you listed.
The use of mangroves has become popular lately. They remove nutrients and have little chance of going sexual (just make sure you remove the leaves if they fall off). thats the plus, the down is that they can be hard to get and a bit pricy. Also they will take a bit of toll on your magnesium level eventually so you should always monitor it if you are using them. Personally I am just about to try them my self
The use of sea grass is another good choice. They are a little more hardy then regular algaes and will not go sexual as much. But like Calurpas they cell structures are leaky. What this means is that...Hmmm ok example..for every 100PPM of nutrients they absorb they leak out about 30% of them constantly. (thats a rough example). This is however not to bad concidering other macro algae. They make a great pods
and larvae factories. The shape of the leave and so on really sets the mood for the happy hour. One other pitfall is that they require about average lighting (as do mangroves).
Macro algae. Depending on the type they can really aborb nutrients, however they also because of the cell nature release alot back in. They tend to go sexual alot more easy then those listed above. And when you harvest it you should remove the whole plant, otherwise they will dump alot back in at that time. From experence (torture actually) i would suggest staying away from anything that has holdfasts. Here is some further info on various algaes/calurpas and thier growth rates (the ammont they grow is directly related to thier nutrient uptake). now when viewing this you have to remember to weight the good (ammont they uptake) against the bad (the ammount they go sexual or leach back in)
Halimeda: ~2% / day (10-20 mg
Dictyota: ~ 10% (50-100 mg
Padina: ~ 10% (75-100 mg
Caulerpa: ~ 10% (50-100 mg
Thalassia: ~1.5% (10-15 mg
Palmaria: ~15% (doubled in 1 week)
Enteromorpha: 20% (7 fold increase in 1 month)
Gracilaria: 6-10% / day
hope it helps