It's great stuff. When it first came out, I had a lady come into the shop who had bought a 55-g tank at big-box-pet-store and 40 fish - ON THE SAME DAY (freshwater, but still...

). Of course a week later when they were all gasping and their fins were clamped, she found me...
I told her to take 35 fish back... big-box-pet-store wouldn't take them. So I fixed her up with some Prime to bind the ammonia, do some water changes and cut back from feeding 3 times a day (!!!!) and gave her the free sample of Stability that the Seachem rep had left me - I figured she had nothing to lose by trying it.
In 2 weeks, her water was PERFECT. She did lose a few fish, probably due to the crazy ammonia spike that was happening when she got with me, and possibly some due to compatibility issues, but over 30 survived and the tank stabilized after that.
I do NOT recommend going too fast and overstocking like she did, but if Stability could help solve that problem quickly, it certainly can help establish a new tank when done properly.
Jenn