Be aware that the AvFab seats have, effectively, zero resale value. The seats they sell are only legal for the specific serial number aircraft they are installed in. If an AvFab seat is bought used, the only legal way to install it is to return it to AvFab so they can "recertify" the seat. Their cost to "recertify" is about the same as buying a brand-new seat.
The OEM seats can be installed with just a logbook entry (no STC - they're a stock part). However, there were slight variations through the years, so getting the correct one for a particular year/model is sometimes a bit difficult. Often the seat-belt and associated hardware is missing.
For the price, I've seriously considered owner-fabricated. For really young kids I would just strap a car-seat to the baggage compartment floor.
