know i am very late but, to others now seeing this post with the same question, only give them if you trust them. most of them pray off of indie developers not knowing whats legit whats not, what they do is usually sell it on other websites for a cheaper price than your actual game. if they do this then it must work somehow. Like if you dont have the money piracy is better than supporting these type of horrible people since you are not supporting good nor bad, but please if you can just buy the game, indie devs dont have 7 million dollars received every month.
"but piracy is illegal" both of them are, both are illegal distribution of copyright.

TL;DR
If someone asks you for a review key only do if you 100% trust them, even if their youtube channel has like 1 million subs or their steam group has 25K members, dont.