I would highly recommend Codingame. As a non-technical person (I am not a developer), I am able to send and interpret results in a very easy manner.

the fact that i can source developers, then test them on the same platform. It's a game changer. Also, i'm able to get an very nice insight on the level of the candidates by looking at the score (they compare with whoever took a test on this platform). They have started to integrate games too instead of problems, which makes it a lot more fun for develoepers/candidates.

I love the fact that we can test an unlimited amount of tech candidates, on top of being able to compare scores within a campaign, or against all the developers ever tested (comparative score). I also like the interface, and the customer support. They've added a sourcing feature which is very promising. I had a couple of interviews thanks to this, and with a very limited amount of money invested, compared to the cost of an agency.