Cons .... I don't know.
I can tell you that I just finished my cycle within 2 weeks (yes yes I know, some will say no way, BUT it is true). I did the "fishless" cycle with 40lbs of UN-cured LR
. After a week my Shrimp was completely gone and my readings were all over the place. My friend came over and brought me a Yellow Tail Damsel and Some stuff called "NitroMax" (basically a jumpstart). After a week of solid Ammo and Trite reading my levels started falling and FAST!!!!
A week later I had brown Diatoms covering the rock and sand ... I took some water to my LFS
to double check my test readings and sure enough my tank was ready for a Cleanup Crew!!!!!
I would definitely say they are a great product to use, make sure you use them according to the directions and definitely keep an eye on your water parameters.
Everyone has a different success story, what works for some may not work for others. In the end we all strive for the same thing ... A happy tank!