IE10 is the least used version of IE (behind 9,8,6 & 4! : https://analytics.wikimedia.org/dashboards/browsers/#all-sites-by-browser) with 0.07% of page views.
It is quite similar in features to IE11 but does still have some bugs that don't affect IE11 (https://phabricator.wikimedia.org/tag/browser-support-internet-explorer/) and is much harder to debug as the F12 tools were only updated in IE11.