From what I understand, they use ultra sonic cleaning, which does get them cleaner. From what I've seen it's only important on the older pintle style of injectors which have a poor design and are prone to clogging since the gas is only sprayed out of one hole. These newer disc style injectors are much more efficient, clog less, and are much easier to clean. Have I compared an injector cleaned by Mr. Injector and one cleaned this route? No. Using this method has always worked great for me with no problems.
Pintle style on the left, Disc on the right:
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