I've actually been using Farfard seedling mix (also at agway) for the first 2 weeks and going into that compost mix on the first repot, and using it all the way through.
I'd actually recommend 30-40% perlite instead of 50- I have to go make sure it's written that way in the manual. But it is a fine mix for all post- seedling life stages. If you want to use it for seedlings, break it up really fine and flush it once before use.