Phylodog, I will loan you my RMR'd 19, and let you side by side them to see what you think the 6 second mount vs. a milled slide has to offer. Other than the cost of milling. My theory is, a milled slide equipped with an RMR, allows you the ability to not change your manipulations, therefore, adding to the "hit" probability? An added bonus, a properly milled slide allows the use of a BUIS, for lack of a better pistol-centric term.