I used it to start my last tank a year ago and it worked great for me. I used a piece of shrimp in a mesh bag so there is a constant source of ammonia. I still waited the traditional 3-4 weeks just to be sure and had no parameter problems.
I tried to cycle with Seachem Stability, and after weeks of dosing and testing I was getting nowhere fast.
I ordered my one and only and the cycle happened in 7 days! I waited another 7 days continuing to dose the system with the ammonia and test just because I could not believe how well it worked. After a large water change to bring my nitrates down I added my first fish and I did not loose it or any of the others that followed (until an unfortunate tank move). I would absolutely recommend it and I would order it direct from Dr Tim's web site. I would not buy it from Amazon or a LFS, as this stuff does have a shelf life.