I use NSW in my 20G and love it. I did notice that I have to supplement iodine sometimes, but I am really conservative because the test is so involved, I worry I am not getting good results and don't want to over do it. I actually think this would be the case for me for anything I had a tested irregularly.
The only thing I have to be carefull about is to buy way in advance, once I went to the store a couple of days before water change time and they were out. I have no backup plan - so I always stock 20G in case of a dire emergency.
sara