I bought this for my 6 gallon book shelf tank, and while it is a little big for it, I love it. I can just fit it into the tank, but I do not use the spray bar. The suction cups work well and keep the filter positioned nicely. The only frustration with the suction cups is that if you are not careful in mounting them they slip and you will not get it where you want it (since I have little room to play with, that was important). Also, if you do not apply careful (VERY careful) pressure, you will cause a slight seperation between the impeller unit and the filter base...which leads to my main gripe and the reason why I did not give this 5 stars. The two pieces come apart too easily when trying to move things around. The suction cups should have a lift off tab, because they really stick.
As for circulation....you will have plenty. It is a pretty powerful little filter and creates a strong current when fully open. The beauty is that it has a little plastic valve that controls the flow and works very well once it is set. Setting it is another point of frustration....but once you get it, you won't have to play around with it and you can forget it. I tried several different mounting options both horizontally and vertically and finally settled on the traditional vertical mount. I also bought the carbon inserts....pretty much a waste of money and I got pieces of carbon on my white sand. A MAJOR pain. I am not deducting from this rating, because it is not part of this set up, but rather an optional purchase. Still, if your tank is cloudy, chances are you need a good amount of activated carbon....here's a tip. Get an old nylon stocking, tie one end. place enough carbon to fill the slot and tie the other end. Easy and cheap and very functional Don't forget to rinse it a bit before putting it into the tank. The little cartridges are just not enough and too expensive.
I did have a problem with sound as well, as if it were grinding gears, but I think the problem was air. I completely submersed the filter, and angled it to make sure all the air got it, and sure enough, no more grinding sound. I will also mention that this was one of those VERY rare times that I did not look to Amazon first and bought this at a local (well known) "pet company." Serves me right and lesson relearned...Amazon has it for half the price and free shipping!
This is very quiet as long as everything stays FULLY submersed. I like the filter box, as you can put your own media in it, which I recommend, as I mentioned with the activated carbon. If anything changes, I will update. So far, I like it!