I start with FFOF as a base, and then I amend it to make it stronger. Sure, it'll work by itself OK in some environments and setups, but not mine.. I want a water only mix start to finish, and FFOF provides me with a good base to start from. It's convenient, easy and 12 bux a bag.
I have it tested so that I know exactly what I'm starting with, and what I need to add to bring it up to my standards. At 25 bux, it's cheap insurance to ensure I wont have any problems.
You'd be surprised how much FFOF can vary.. I've found that bags you pull from a single pallet will be close to the same in regards to test results. However, when you go back to the store a couple months later and grab from a new pallet, test results can be very different.. Big changes in PH, PK and saturation ratios..
Sure, test results can vary for other reasons too.. depending on how sample was collected, prepared, lab variants, etc, etc.. But I've been doing this a long while and am fairly confident in my collection technique and soil test vendor - it's my strong assumption the variations I see are related to the product, not the testing process.
I just had another FFOF test come back, I'll post it up next time I'm @ my PC