I routinely use independent instructors and mechanics.
CFI’s I use are all very experienced in multiple types of aircraft including jets and airlines and have many years of real world experience outside of the training ‘bubble’ of Bend. The kind of training I need for BFR’s is highly aircraft specific (Cirrus) and is safety critical that the instructor knows the aircraft and its highly advanced avionics at least as much, but hopefully more than I do. This makes me a safer pilot and provides income opportunities for the instructors. I would not hire any CFI from one of the flight schools that has probably never flown further than Klamath Falls or Portland. I find that younger CFI’s coming out of larger programs tend to have a know-it-all attitude and have something to prove when flying outside of the ‘system’
As said, mechanics provide another set of eyes. Many independent mechanics are specialized in certain aircraft types, especially important for experimental’s and vintage aircraft. Current shops on the field are seeing a mechanic shortage and have a lot of mechanics in training that do not have a great wealth of knowledge or experience.