I have two C-530's on my 155. No leaks, no problems, huge media capacity and as 1bigdovii stated, virtually no bypass. I know there is a huge FX5 fanbase here and I'm not going to suggest that the 530 or 360 is a better filter, but consider this, virtually no bypass out of a filter that could cost more than $100 less than an FX5! Nevermind a comparable Ehiem. Would I have liked to have installed a couple of Eheim Pro 3 2080's in my stand? You bet! But at more than double the price each (plus the cost of media for each) I opted to pass.
To be honest, I was going to get two FX5's for my 155 but I got a great deal on my two C-530's. If I had it to do over again, I'd probably get one of each (FX5 & C-530). I wouldn't recommend a C-360 (or two depending on tank size) for anything more than say a 125 depending on the bioload.
Another plus is that Marineland throws in the sponges and media with the filters. Is it up to Eheim quality? Doubtful (I personally just used the ceramic rings, sponges and polishing pads in mine and replaced the carbon and bioballs with two levels of Eheim Substrat Pro). I don't remember if Fluval includes the media with a new FX5, so Im not going to try to draw a direct comparision in that respect. I have no experience with the Rena product line, but have heard good things. I did consider buying two XP4's for a few minutes, but the C-530 deal along with some good reviews (
www.oscarfish.com) pretty much sealed it.
From my experience thus far and those I been in contact with on the subject, it seems that Marineland's customer service is second to none. Can Eheim say that? IDK, just asking. Iv'e also been in touch with people who think the only Fluval filter worth even considering is the FX5. Again, IDK as I have no experience with them.
Bottom line, I think the ML C Series canisters could be a decent cost effective solution depending on your setup.n my opinion, If you put a C-360 and say an Aquaclear 110 on a 75gl housing a single large adult Cichlid, you'd have a pretty damn good setup.
Have at it!