I do use some MMO in the fuel. I believe it does have benefits, even for a modern car, and I don't know of any disadvantages other than the approx. $0.60 per fill-up at the recommended dose.
It is both a lubricant and a solvent, whereas most additives are one or the other.
Red Line SI-1 is also both a top-end lube and a solvent, and is probably a much better solvent (containing, as it does, fairly large concentrations of PEA), but is much more expensive.
For injector cleaning specifically, I do not believe MMO is effective.