20 million:1 contrast ratio is dynamic contrast. It's a meaningless marketing number. Basically it means the monitor darkens when you're displaying all dark colors, brightens when displaying all bright colors. It's useless if you're displaying both dark and bright colors at once.
I was able to find a Dutch review of the monitor which puts its true contrast ratio at a respectable 845:1.
https://translate.google.com/translate?sl=auto&tl=en&js=y&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fnl.hardware.info%2Freviews%2F6035%2F5%2F23--en-24-inch-monitoren-review-een-voordelige-verse-blik-aoc-e2460sh&edit-text=&act=url
Based on that review, the only real weakness to the monitor is that it's a TN panel, and the colors shift pretty quickly with changes in vertical viewing angle.