I bought 6 mgn12h from the recommended vendor in hopes of getting 5 good ones. They have arrived (separately in 2 packs of 3)
Of the 6, 3 are really smooth with no cleaning. Two have become much smoother, though still not as smooth as the 3 after lots of cleaning and lubricating. One I'm not holding out much hope to get smooth and I can't visually see the flaw.
My plan is to use the good 3 nd goodish 2 and see what my print quality looks like before spending more on the Hiwins.