Just to answer a few quick questions you may have...
Does it work? Yes.
Does it use suction cup/s? Yes.
Indicator Light? No.
Adjustable temperature? No.
Fully Submersible? Yes.
Size and Color: I'd say it's around 4in x 1in with a 1/2in depth, color is black.
I have been using the Aqueon mini heater for Mr. Moto (my betta fish) in his 2.5 gallon mini bow aquarium (acrylic aquarium). Since Ebo (my newest betta) doesn't have a heater in his habitat it was reading at 70.2F, while Mr. Moto's aquarium with the mini heater was at 76.8F. That being said Aqueon's Mini Heater raised the temperature 6.6F, which seems to be a nice temperature for a small betta tank like Mr.Moto's. Keep in mind that if your tank water is colder/warmer (depending on the outside temp) or your aquarium size is bigger/smaller than the heater may not give the same readings as mine as their are many different variables to consider when using practically any aquarium heater. Their is also no adjustable dial on this device to lower or increase the heat so while it may work for some it may not work for others, but I find it's perfect for my 2.5 mini bow aquarium setup I have. I definitely recommend trying it if you do have a small aquarium setup such as 5 gallons or less.
As a side note this product claims that if you leave it outside of water and plugged in that it has a 'thermal safety shut-off' that will initiate, and the unit will then be rendered unusable after that. As always with aquarium heaters, give the device several days to work in your aquarium setup before judging its performance as heaters can take up to 48hrs to gradually heat the aquarium, this is done purposely as to not shock your fish and cause them to get ill.