Bargain! If I was shooting APS-C Canon I'd get one.
Just a note, you mention in the vignetting section how bad it is at f3.5 but it should say 4.5.
This is even better than I expected from the MTF curves Canon provided. I thought it would be a f/8 lens. That it can be used wide open with minimal impact is a bonus.
<a class="bbc_url" href="http://snowporing.deviantart.com/">dA</a> Canon 7D2, 7D, 5D2, 600D, 450D, 300D IR modified, 1D, EF-S 10-18, 15-85, EF 35/2, 85/1.8, 135/2, 70-300L, 100-400L, MP-E65, Zeiss 2/50, Sigma 150 macro, 120-300/2.8, Samyang 8mm fisheye, Olympus E-P1, Panasonic 20/1.7, Sony HX9V, Fuji X100.
With the EOS 100D, 10-18mm IS STM, 18-55mm IS STM and 55-250mm IS STM Canon has a pretty impressive light weight DSLR setup available now, which indeed is very affordable.
Only downside I see of this lens is the light fall off, the weight saving has to come from somewhere I guess. That is then the only thing to keep in mind (besides the CA) if I would want to modify one for FF (which would basically turn it into a 17-18mm f5.6 prime with IS and STM).
Nothing to say but an absolute bargain, without the usual having to stop down at the wide end.
How on earth did they do that? I guess they are unlikely to tell anyone!