In a low-tech tank surface agitation is a good thing. The high-tech guys avoid it because they are trying to maintain an unnatural imbalance of gasses in their tank. A low-tech tank is just trying to maintain a natural balance. As plants use CO2 throughout the day you need to replenish it. The only low-tech source of CO2 is the air. Just like surface agitation provides oxygen for fish as they pull it from the water surface agitation provides CO2 for the plants as they pull it from the water.
As for the filter, I'm quite happy with the Tom's Mini Canister. It does a great job on a small tank. It is a pain to service. And it needs to be serviced pretty often due to its small size. But I doubt you can beat it for the price.
Having said that, I just ordered all the stuff to build a mattenfilter for our twenty-gallon. It's cheap, low maintenance, and seems to be quite effective from what I've seen. Mine cost more than the Tom's canister did. But that's because I'm using a powerhead to run it instead of an airlifter. It's still cheaper than a canister or HOB for a twenty-gallon.