Coast of Maine Stonington Soil

Has anyone tried Coast of Maine Stonington soil? I've read a lot of good things but I've also read that it's a little hot. I was thinking of using 2 parts Stonington and 1 part Happy Frog or maybe Roots Organic Original. The company claims it's a super soil and you only need to add water. That seems too good to be true but I'd like to give it a shot anyway. Also, is there a minimum container size? Would a 3 gallon be too small for this type of soil?