When you open the box, the Whisper 40i (or it's smaller siblings) don't seem very impressive. It's not much more than a oval plastic bucket, with another bucket (containing a motor and pump) snapped onto the bottom. If you looked at one and thought "this can't possibly work", you would be so wrong.Perhaps they work as well as they do BECAUSE they are so simple, and so have little chance for things to break. The pump sits IN your aquarium water, so it never needs to be primed. You plug it in, and it begins working, filling the upper bucket, where the water flows through the filter pad and spills back into the aquarium. No priming necessary ever, including after a power failure. When the power comes back on, it just starts working again. It's a shame that every hang-on-the back power filter can't make a similar claim, some unfortunately will lose their prime and/or fail to restart, resulting in unhappy fish and sometimes a damaged filter.There are no adjustments for flow, so these only run at one flow rate. Inevitably, some food can get sucked up if you let it run while feeding. I have the filters on a separate power strip, so when I feed my fish, I just use the switch on the power strip to turn the filters off for an hour or so. Easy solution and prevents the filter pads from clogging so quickly.There is no top or lid (unless you buy the model intended for reptiles), so the filter pads just sit there exposed. This means that the water in the filter is fully aerated as it passes through the pads. It also means that no other internal filter is as easy to change pads when they become clogged. The top edge of the pad is above the water line, so you just grab it with two fingers and lift it out. You don't have to disturb the suction cups or hanging bracket at all. You don't have to put your whole arm down into the tank. Maintenance which is easily performed is more likely to be done when needed, so easily changed pads are more likely to be changed when clogged.You have options for how you want to attach the filter. The box includes two suction cups, and a newly designed bracket which hangs over the edge of your tank. I use the bracket, as it's adjustable for height and I don't have to worry about suction cups losing their suction.The filter pads are the Whisper bio-bags, which amount to a thick fluffy poly bag, over a plastic frame, with carbon granules inside. Replacing these is simple, and if purchased in a 12 pack from Amazon, cost about 60 cents per bag.I used Emperor filters for years, and in my experience, these bio-bags work a lot better than the filter cartridges for Marineland products and cost much less to buy. If you rinse them under tap water, which is easily done, the cost is even less. Rinsing the bags doesn't disturb your biological bacteria since they are on a separate part (resembling a hair brush) which remains in the filter when you remove the bags.You do have some flexibility with regard to media options as well. You don't have to use the carbon which is included with the new pads. You can put anything you want inside the bag, and if desired, transfer it to the new bag next time you change them out. You also don't have to use the separate biological "hairbrush", and if you leave it out, you have room to put another media bag in it's place, with ceramic rings, or whatever else you can think of.I have four of these, mounted on two separate tanks, one 55 gallons, the other 75 gallons. All four of them are not quite silent, but very quiet. There is a soft, low hum from the motor windings, a little bit like a transformer humming. At first there was also a faint sound like air trapped somewhere, perhaps cavitation in the pump? But these sounds are hard to hear, and not distracting. And the cavitation sound went away on it's own after a few days. I can hear the soft humming sound if the room is totally quiet and I stand near the tank, but if there is any significant sound from conversation, crunching breakfast cereal, a radio or TV, etc, then they are drowned out.Some of the complaints others have mentioned in their reviews sound a bit like operator error to me. For example, one person said the filter overflowed and sent water over the back of the tank onto the floor. Clearly, the filter was mounted too high....mine are mounted with the top edge 2 inches below the rim of the tank. When the filter pad becomes clogged, it WILL overflow, but into the tank, not out of it.Some describe loud mechanical noises, which sounds to me like a bit of gravel, or perhaps a snail, found it's way into the pump impeller. Yes, this can happen with any filter, regardless of brand, but it's easy to repair. In these filters, the bottom just snaps off, exposing the pump impeller, which is then easily removed for cleaning.And some have complained that the filter "stops working" after some months of service. Again, this is likely due to a need for a cleaning of the impeller and the recess where it sits, where debris or gunk sometimes builds up and prevents it from rotating.On a benefit/cost basis, these filters look really good. They are made of a tough, slightly flexible plastic, so even if you drop one on the floor, it is unlikely to break. Parts for Tetra/Whisper filters are readily available everywhere. And the results are as good as any other filter I've ever used, regardless of cost.The first attached photo shows two mounted in my 75 gallon planted tank, which contains two Nigerian bichers, and two Pictus catfish. The second shows two more in my 55 gallon community tank, with various tetras, cory catfish, and loaches.