Although the system is slimmer than most typical HOB (Hang On Back) Power filter systems, I actually find it to be wider in comparison. This filter is suppose to filter up to 10 gallons of water but I'm not sure how true that claim to be. I do not understand why they make a semi-clear filter system rather than making it completely clear as it's a black transparent color (so, it will only flatter black background aquariums). I could see some people liking the semi-transparent look just because they want to view inside the intake tube or perhaps see the filter cartridges, and with it being semi-transparent any filter buildup would be less noticeable had it been completely clear (much like with the Red Sea Nano Filter).
I find that the filter motor which is attached to the base of the units intake tube (rather then inside the unit as with most HOB filters) unappealing as you're stuck looking at the motor inside of the aquarium (which is not clear nor transparent, but rather big, bulky, and solid black in color). However, this does leave more room inside the filter box which will allow you to add in additional media, or you could even add in a small aquarium heater although there is no hole for a power cord to go through so you would have to leave the tank lid off if that's what you wanted to do (or possibly drill a groove to fit the power cord). Another good thing about the motor being at the base of the intake tube is that it requires no water priming to start the power filter, which is good in case of power failure. I also like that this motor comes with an attachable pre-filter which will keep fish from getting stuck onto the intake tube. I do find this unit to be pretty quiet compared to a lot of other power filter systems I've had in the past which may be because the motor is attached onto the intake tube and also because the waterfall bridge seems to be fairly long so that you could partially submerge it underwater thus reducing water noise. However, the motor tends to cause a lot of noisy vibration inside the tank and may require constant re-adjusting, this is the biggest flaw I have found with this unit. You can also adjust the length of the intake tube slightly by sliding the base of the intake tube up or down. This unit also has an attachable clip under the filter box so that you can level/adjust how the box rests on the aquarium. There are also some run-off grooves around the filter cartridges in the box so I don't think water would ever make its way outside of the filter box and onto the floor.
The filter cartridges this unit comes with is the Marina bio–carb and bio–clear, and I do like that this has two separate cartridges however, I'm not sure that water will flow through both of them at the same rate since the cartridges don't overlap one another inside the box (so far it looks like more water runs through the filter cartridge furthest from the intake tube). Thus far the filter media seems to do nothing in terms of discolored water. The bio–carb cartridge states to remove pollutants and odors, where as the bio–clear states that it includes zeolite to absorb toxic ammonia and reduce fish stress (I have not noticed any traces of ammonia in my new setup thus far).
The main reason this power filter is perfect for betta aquariums is because it has an easy to adjust control valve (although you do have to remove the lid to reach it, but not a big deal) inside the filter box on the intake tube which allows the water to come out as either a trickle or a more turbulent water flow. Overall, I would definitely recommend this filter for small betta aquariums (probably won't fit properly on tiny cube tanks though), and thus far I am really loving it over my old Red Sea Nano filter I had prior (and I do think it's fairly difficult to find a low flowing filter for betta tanks) although the Red Sea Nano would be a better option if you do have a tiny cube aquarium (since the Red Sea Nano is much smaller than the Marina S10).