Cant speak for reliability but can say I've ordered a couple games from CD keys. They send you an email after payment and you enter the key, in my case, onto steam. There's a section to enter keys. Then the game downloads. The games I ordered were older, so not sure it'll work with newer games.
Another good place is https://www.fanatical.com/en/on-sale I spent the holiday just getting $0.58 older games to less than $20.00 new titles. I just check daily as the inventory looks the same But they throw in some gems here and there. I have only bought Steam games but they also sell Origin titles on there as well.