Tamron 18-200 mm VC for EOS M??

I have the III version of the Tamron 18-200 for M cameras.  Built like the proverbial tank - a bit larger and heavier than the Canon EF-M 18-150 F3.5-6.3 IS.

I would imagine (somebody correct me if I'm wrong) that the II version, along with the converter, would result in a much larger profile.

IQ-wise, I would say they are about the same.  The M version is a very good all around performer, but like any other super zoom lens that covers both the wide and telephoto end of things, you lose clarity somewhat due to all of that glass.  For example, I can attach the Tamron 18-200 (for EOS M) and take a series of photos of scenics, foliage, trees, grass, or what have you.  I then can attach either a good copy of the Canon EF-M 15-45 or the EF-M 18-55 and capture the same scenes.  The end result is that the images taken with the Tamron have less clarity - details are rounded out (smeared a bit?).  Most obvious is when you look at grass in a yard for example, they are smeared and individuals grass blades are difficult to find, whereas the same scene with the EF-M lenses mentioned above, would net you definitive grass blades.  If this is not important to you, then you'll be quite happy (with the III version).

I used to "swear" by my Tamron - until they lost my original 18-200 which I sent them for a firmware update so it can function with the M5 and above.  It took them a month to replace it, and the end result is that the copy they sent me (even though it was new) is clearly not as sharp as my original one.  I now rarely attach it to any of my M cameras anymore.  I was debating about selling it, but then there will come the time when I will need an all a-rounder for a trip or something, and this one will do the trick.  Now if something better comes out, then I'll sell the Tamron.

Remember, these types of lenses result in severe compromises and are really only good if you need just one lens to cover most focal ranges (less the ideal clarity that you would expect).