[Slick Fork]

I think the thing to take away from the cannister vs no cannister discussion is that IF you clean them religiously, they're not necessarily an evil place to run carbon and GFO and if you had one already I would not dissuade you from using it.

However, since you don't already have one there are much more efficient ways to spend your money. Yes:
- You can run carbon adn GFO in it but you can also run carbon and GFO in a HOB filter that is easier to clean.
- You can put live rock in it, you can also put live rock in your tank.
- You can use it to increase flow, powerheads do this much more efficiently
- You can use it to "add a gallon or two" but really, on a 50 gallon tank I think the argument could be made that a gallon or two isn't really going to make a noticeable difference.

So really, since you don't already own one... I think the question you should be asking is not "Can I get away with using a cannister filter?" but, "Will spending money on a Cannister filter instead of other things benefit me somehow?" As an example I'll use J&L aquatics pricing (I know you found the 405 on ebay but I have no idea what the price was so we'll stick with J&L) A fluval 405 would run you $199. For that kind of money you could buy 2 Koralia 4's and a phosban reactor kit to run carbon & Rowaphos.

This can be a VERY expensive hobby if you let it. The key is figuring out which investments will get you the best returns, otherwise you could spend a fortune throwing good money after bad