How do you get the TC function to come up. I didn't know that was possible... and even now that I see it... I don't know how to replicate it.
I'd suggest a Canon TC. As you rightfully pointed out, this means your new purchase is also good to go with your other Canon kit.
There doesn't appear to be much in it between the two when it comes to resolving detail:
But of course the 70-200 and 1.4 combo has more reach, and it gives you options with your 5D2 - 70-200/TC and 135/TC, whereas for you, buying the EF-S lens is a one horse trick.
The 2x TC will potentially resolve more detail than the 1.4x and cropping, but the lack of AF on either of your bodies with the 70-200 and the images the 135 would produce make it largely worth ignoring for any purposes other than shooting distance objects using the M with manual focusing.
Thanks! I never knew you could use teleconvertors for TDPs lens image quality comparison tool! Yeah theres not much difference, though the EF-S seemed to be slightly better in the centre. A little PP sharpening should sort that out. Yeah I think I already answered my own question but still good to hear it from someone else!
So you don't recommend the Kenko adaptor? Any reason for that? I feel like the Canon is over priced a bit. And for my purposes v2 should suffice right?