well air pumps are the noisiest filters you can get. the xp1 is gonna be tons of filtration for a 20gallon, but yes it'll work, and be quieter than an airpump driven system.
Don't know enough about RO
units...but most freshwater tanks don't need them. If you can list your tap water specs (pH, hardness in Kh
, and nitrate/phosphates) we can tell you if RO
is necessary, useful, or just a waste of cash.