I had an aquaclear power head filter, and personaly, I'd say it's not the best because it only has one, or maybe two types of filtering, the typical, mechanical, and if you have carbon, then it also has chemical one, you can adjust your desired water current with or without air bubbles, it comes with a hose that sucks the air, there is where you could add CO2.
Regarding to the other question, I switched the power head to a AquaClear power filter (HOB) and works great for me, it has three types of filtering, you can adjust the waterfall and leaves the water very nice looking. If your tank has 10g then you can only buy the 20g filter, I think for 40$-60$ or something, the only problem I faced was that it sucked the foot one of my poor apple snails and died "drowned", it will easily suck any RCS and/or small fish, the solution? Adjust the filter to have a middle-high current and place a sock or a foam around the tube and tie it up with a rubber band.
There is also the fluval HOB, it's cheaper and works great too.