M 40-150mm R for $100 worth it?

Going way back, you have the 4/3 mount 40-150mm f3.5-4.5- fastest aperture but slowest focusing on m43 This lens is huge compared to the ones that followed. Has a metal mount (all the rest are plastic)

then there was the 40-150 4-5.6 - also 4/3 mount, but CD-AF compatible, so a little faster on m43 than the first version. Obviously, the 4/3 versions will need an adapter to use on m43

m.Zuiko 40-150mm f4-5.6 ED MSC - two versions:

First one has a silver base(on black version), lengthwise ridges in the zoom band.

newer model has 'R' after 4-5.6 on the barrel, is all black, and has a different zoom grip pattern.

Any internal differences between the m43 versions? Maybe. The m43 versions are likely quite similar internally to the 4/3 MkII version, while the original 4/3 version is the most different.

BTW, 'R' may just stand for revised. while MkII is just a convenient notation on the forum and is not be used by Olympus (although I think they did use that designation for the revised 4/3 mount 14-54 which added CD-AF compatibility.

--
Art P
"I am a creature of contrast,
of light and shadow.
I live where the two play together,
I thrive on the conflict"