Tested it in my excel cap--1 pump is approx 1ml.
I've been using Pfertz macro/micro, K and root tabs the past two years. After the first few months of use, I tossed the remainder of my Flourish in the trash as not being worth using. I do think the Flourish root tabs have a slight leg up on Pfertz tabs, but it could just come down to the size of the tabs.
That said, I'm moving towards using dry ferts now. My tanks are potassium hogs so it's nice being able to customize the dosage; I'm still using my old Pfertz K bottle (being all handily labeled and all) but it's at a 2x stronger dosage per pump. Once my macros and N are gone, I'll move to dry on those as well.