The biggest issue with transitioning to an airplane that is not the typical flight school type is getting a checkout from someone who actually has experience in operating the type and can give you the tips and tricks and the gotcha’s
Generally, a very valid concern. Happily for the OP, the instructor he has contacted in this case (Derick Gunning) is very familiar with the type, I've met him, and have great confidence. But yes, there are numerous GA types for which "flying school instructor" training is simply not practically available, the training has to be sourced from type familiar pilots.