As far as I know, the main differences (400 v 200) are:
-- aluminum vs. steel brake lever
-- two-finger vs. three-finger lever
-- caliper design/construction/appearance is in line with Shimano's Deore+ level mtb calipers vs. blocky/crude/'industrial' look of the 200s.

That's about it. I owned/used the 200-series ones before replacing them with XT 8100. They (the 200s) worked perfectly well -- they look clunky, lever rattled around a little, but they are perfectly good brakes.