For what it's worth, this is what I know.
Like with most instructors, I know people in the baseball world that love him and those who think his style of hitting (rotational) is only for certain types of players.
LJ Hoes (former St. Johns HS standout, 3 time All-Met selection, and '08 Balt O's draftee) was and is a student of his.
I've never met the man, but I've heard he's a nice guy. I've watched players play who are students of his, as my son played with several of them. The stronger players physically, do well; however, those who are not as physically strong, struggle with rotational style of hitting.
It never hurts to try something out, and if it isn't a fit, to move on.
I personally like Derrick Hacopian of Maryland Baseball Academy (Gaithersburg, MD) or Matt Knox of Elite Baseball of Lancaster Pennsylvania http://www.elitebaseballoflancaster.com/. Neither teach rotational hitting, although that doesn't mean RH won't work for you. Again, I use LJ as a prime example of a player who prospered under Mr. Johnson's direction.
Peace and God's Blessings...
Shane