I certainly don't have the experience that others do, but I've bought and used about half a bottle of Millwax on a few 80's SS games and a System 3. My only complaint is that it's runny and gets into everything. I didn't notice that it put a particularly great shine on any of my machines, nor did it greatly improve gameplay. I probably didn't put as much effort into it as Juggernaut- his machines look incredible!
Millwax was recommended to by by a repair guy that came to my house and did a bit of board work for me. That was quite a while ago. I took his word and bought a bottle from PBL or somewhere similar.
Not to be a butt-kisser, but I really trust what LTG says- especially considering he's a been a part of the pinball fabric for around half a century (?).
I don't plan to throw away my Millwax, but I certainly won't be buying another bottle.
Also, if I found out that millwax was used to maintain a pin I was thinking about purchasing, it would not deter me from purchasing it.
To each his own- but I'll personally be following LTG's recommendations.