I had really bad luck with them. Alk swing like crazy RTN/STN.
I decided to go back to phos and carbon wich has worked out much better for me.
Keep in mind this is only my opinion. Some people have had great results. You just need to decide if it is worth the risk.
I set mine up when i set my tank up .. Just added a fourth of what they suggested .. Havnt added anything since than .. Just added a little gfo in a reactor .. Will test and see if i need more pellets in a week or so .. Gl