Why leave a review after a mission with a freelancer?
The freelancers' reputations are important, and via Malt, they can put their expertise forward, helping to build their e-reputation. It is thus thanks to the clients who trusted them that they can develop their activity and capitalize on their reputation.
The freelancer gave you quality work, allowing you to complete your project ? Then why not say it and recommend them to other companies ?
If the mission went very well, you can also leave the freelancer a bonus, by asking them to change their current quote before confirming the end of the mission :)