its relevent to know whether it has bad effect or not in any circumstance but if you want to do a fish only marine system using canister filters there good but you only really need one if you get loads of whittespot or algea overwise they wont do much but kill the beneficial bacteria (which wont be just filter bacteria.
this is from a book that is a few years old but still a very good reference
natural and neccersarry diet unknown. Appears to eat and may accept meaty foods, but seldom survives more than 18 months. appears to die of malnutrition.
MARINE INVERTEBRATES Roanld L. Shimek, Ph.D.
as there diet is unknown according to an invertebrate ultra knowledge knowing person, he has got a phd in the field i would take his world in saying that its unknown and most die due to lack of knowlege though apparently they might accept meaty foods like krill
well the member who started the tank was a freshwater keeper so telling him why marines are harder to keep was on topic so actually you are wrong there. its helpful so he knows that water changes each weak are not a good idea and that it needs to be approached differently.
if there is a power cut there isnt much you can do less you have a load of battery powered air pumps and if your power is out for a few hours it shouldnt matter to much so long as you fix it straight away with a water change and addid an airator. this is why i said short term. you cannot heat it, you cannot airate it less you have these soo called battey powered airators and when theres no power in the house its going to be important to sort other things out first.
and yes there are other ways of filtrating a tank though as i said the hold no where near as much bacteria and this is why the berlin method is better.