The Ruger Mark IV is a very fine representation of where Ruger wants to go with their Mark pistols.
For someone to post that ALL the aftermarket parts produced for the Ruger Mark pistols are not necessary, is ignorant as to how these pistols perform from the factory, or, has most likely NEVER had one apart, tested it, or worked on one thoroughly. It's impossible to get any representative amount of experience when you've only owned one Ruger Mark III pistol, let alone never had it apart to see what really does make that pistol "tick".
For one thing: There's a very GOOD reason why there are at least 6 aftermarket producers of better "extractors" than the currently provided stamped steel extractor Ruger has been using for 69 years.
Volquartsen produces many aftermarket parts for the Mark pistols that are "restricted" by Ruger as far as selling individually. Many are only replaced at Ruger on an exchange basis only, so that's why Volquartsen started selling parts for the Ruger Mark pistols, and those parts are, in many cases, better than the factory provided part. For example: The Volquartsen Target Sear will drop-in replace the factory sear and improve your trigger pull from 5½ to 6 pounds, down to a safe 2½ to 3 pounds.
"Caveat Lector" For those on the east coast.........Reader Beware.