Sounds like a bunch of nonsense, and an effort to bleed you for too much money.
We always did checkouts three up. There is nothing scary about stalling / being stalled with a PAX or as a PAX, whether its a 172 or PA28. (It was quite interesting as a rear passenger in a Seneca doing power on stalls. Facing rearward in the club seating with my feet on the other seat, the nose pitches up about 50° and it made for some great views of LA harbour 3000' below my feet
) Steep turns shouldn't be an issue, your mate is a PPL and knows what to expect. Nav is unnescessary in my opinion, and you'd both learn more if you double up....
Cheers