One potential problem with using "seeded" media is knowing and trusting the health of the donor tank. Some keepers won't even seed from their own tanks, but rely on bottled bacteria like: Tetra Safestart, API Quickstart, ATM Colony, Microbe-Lift NiteOut II and Dr Tim's One-and-Only (arguably the best and most expensive). Even Seachem Stability works somewhat.
Or, because nitrifying bacteria are in the atmosphere, you can wait until it literally falls out of the sky into your tank. That's the cheapest but longest method.