Considering he was a free transfer it seems ok
Anyway after one season offer him a new contract and if he refuse sell him for more than 50M (thats if he proves his worth to be a great signing)..
Obviously he wouldn't have come if no clause, so if you're gonna have it, this is the way to do it. 50 million entering last 2 years of contract is a great price, but I expect him to perform above that and sign a new contract with no RC or even bigger price in the same pattern.
So that is why he refused a new contract with Liverpool as they didn't want to insert any release clause but I can't understand why did we insert release clause if player wants to leave he needs to only ask to leave and the management will fulfill his wish.