Moly is one of those things that comes and goes in the shooting world, and moly coating has been around for many decades. Its latest resurrection began in the 90's, and many of us competitive and high volume varmint shooters began using it....again for some of us. When barrels are prepped properly, moly allows for extended shooting strings without cleaning as often or experiencing POI changes, pressure, etc. I shot many HP matches, BR and several P-dog shoots that allowed for numerous rounds without experiencing issues related to copper or other fouling.
If home coating, moly can be a mess, but if one follows proper technique, it isn't that much trouble. I have tried the BB tumble method, vibrator, plain tumble, etc, and while some swear by the BB or bearing tumble method, I found the plain bullet tumble did just as well for me. I use a small rock tumbler with a rubber drum to hold about 500 22cals or about 250-300 30cals at one tumble.
Positives "I" found - Reduced bullet drag due to reduced engraving damage at LR/ELR resulting in less drop. Longer shot strings between cleanings. Reduced copper and other fouling buildup. Less POI changes with long shot strings. End of shoot cleaning was easier.
Negative - Can be messy. Clings to everything. Proper barrel prep before and after is a must, especially before returning to non-moly bullets. May experience velocity/pressure DROP with same load as non-moly, so depending on load, cartridge, barrel, one may have to up powder charge a grain or two.