It will work to absorb nitrogen until it is exhausted. In the process it will prevent your filter being exposed to any nitrogen to establish a nitrogen cycle. When the nitrasorb is exhausted, the fish will swim in ammonia until you notice that it has stopped working and get more nitrasorb. Even though it works, it is like raising animals while feeding them antibiotics. They won't get sick until the first day you are out of the antibiotics. On that day they won't have any natural immunities and they will quickly deteriorate.
I am sure the product literature tells you how bad ammonia is and how well the product works. The trouble is they won't tell you the consequences of using the product and its effects on the rest of your aquatic environment.