Yup, exactly- it is too rich for a young seedling. Happy Frog or a cheap seed starting mix from a nursery are much better for seedlings, which don't need ANY added nutes at first.

Transplanting a rooted clone into a pre-fertilized soil, I'd use caution. If the clone was rooted in a plug or peat pellet, or even right into seedling mix or promix, I wouldn't worry about it. If the clone was rooted in a bubbler/DWC/aero type cloner, I'd first plant it into seedling starting or promix and then when it is starting vertical growth, transplant NEXT into the FFOF.
Hope that helps?