My timber frame post sit on solid blocking, they do not extend to the concrete.
I didn't buy a kit, could not afford to go that route 30 years ago. I started with rough cut 8x12 timbers, planed and cut all the mortise and tenons myself. I had about 1000 hours in the framework for a 3000 sq ft house and 1000 sq foot garage. It was raised in a day, with the only issue being too small of a crane for the house bents.