In Ajax's unbiased opinion, your stealership most likely recommended fuel injector cleaning because it is almost pure profit for them-- especially since you did not mention any performance problems. If you are using a quality gasoline like Shell or Chevron, the injectors, intake and exhaust valves, etc. should stay clean for a long time on their own and probably never become an issue.
This is especially true since M6 owners don't tend to keep their vehicles into high mileage anyway, and we drive them hard as they are designed to be driven. Crappy gas like Cesar Chavez Citgo, or Costco with minimal additive packs will ruin engines over time; a quality brand and the cleaning agents in it will start doing their job, gradually, without doing damage to the engine. The above video was definitely an eye opener!
Again, this is only Ajax's unbiased opinion.