I have been considering this lens for months but couldn't quite make a decision. What bothers me the most is the concern of complex distortion. I'm glad that it may be correctable post, but it'd be nice if someone could post some pre and post process pictures.
The other option is 17-40 which is a safer choice. At least the resale value is good. I tried it once. Corners seem a little fuzzy.
5DMK3, 80D, 24-70 2.8L II, 16-35 F4L IS, 100 2.8L, 70-200 2.8L IS II, 35F2 IS, 135L, 70-300L, 70-200L F4, 600EX-RT x2, EOS M, efs 10-18, efm 11-22