Not sure if you're planning on using the canister on a FW
tank. Roka's comments about filter media are great but pertain mostly to SW
If you use carbon yes you do have to change it out periodically same as you would with any other filter. Same goes for cleaning/replacing foam pads etc. I find mine is just as easy to clean as the HOB
(if not easier, it's just bigger). Most modern canisters have a quick disconnect that lets you leave most of the plumbing attached to the tank and bring the filter to the sink. Once a year or so it would probably be a good idea to disassemble everything and clean out the tubing, but again, same would go for a HOB
As far as power outages, well, nothing much happens. The new filters don't lose prime, and they start right back up again, usually with much less moaning and groaning than the HOBs. My power went out the other morning and the only way I knew it came back on was the tank lights, my two XPs came back on without a sound.