"Pretty much everyone needs a skimmer. There are lots of different designs, and at least as many arguments about which one is the best.
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Pros: This thing is cheap and it actually works. A lot of people have complained here and elsewhere online about it not working well, but when it's set up correctly (and one advantage of this design is that it doesn't require complicated adjustment) it works fine. Like any skimmer, it'll require maintenance. (E.g. you have to empty it when it gets full, clean it out once in awhile, and maybe replace a leaking O-ring.)
The big advantage is it doesn't cost $250-400 dollars. Both the company and the design have been around for a few years.
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Cons: It's relatively cheaply made, and it's more prone to leaking than many others. It's not necessarily a faulty design, it's just cheap. Watch the seals. If it's going to leak, it'll leak there. Be sure O-rings are seated properly and not twisted/overly compressed/distorted, or they'll definitely leak. If you get it home, and it leaks, fix the O-ring issue, and you'll fix the leak. (Also, check for leaks in the sink BEFORE you connect it. You won't catch every leak this way, but if it leaks even a little in the sink, it'll leak a whole lot when it's connected to your aquarium.) If you need to, reseat/replace O-rings from time to time, but not if it's not leaking. (I'd definitely follow the "if it ain't broke, don't fix it" advice regarding leaks; however, if it even starts to leak a little, fix it. Even a small leak means something isn't right.)"