I tried out Mazraoui because he fits my team perfectly and have been bored of using ShowDown Darmian for a while now. I like my fullbacks to overlap and get forward, and I thought Mazraoui would certainly be better than Darmian at that. Personally, I didn't really find much difference since I don't tend to dribble with my fullbacks much, and Mazraoui's passing wasn't hugely noticeable to be better than Darmian. The main reason I did not like this card at all is the work rates. The high attacking work rate was great for him getting forward on the overlap, but on the defensive side he was noticeably lacking, or worse, not even trying to get back and my 91 Nkunku was playing RB half the time with Mazraoui refusing to get back after being on the attack. To make the defensive side worse, his physical and defensive attributes are worse than Darmian's too, so for my team personally I just felt like he was a massive downgrade in what I wanted from my fullback, because as much as I like them to overlap, it is obviously a necessity that they can defend as well, and Mazraoui just didn't deliver on that front. I won't even say that isn't because his defensive stats are bad either, he's just never in the position to use them because of the workrates, so Darmian is back in my team for now until I can afford a different RB.
However, I will say that for 25-30k, there aren't many right backs that have as good attributes in the game for this price range, it's just that for me already having Darmian in the club and liking him a lot, this card performed nowhere near as well for me in terms of what I wanted from my RB.
I'd say if you can link him he's probably worth a try, and you might find him a lot better than I did, but I really didn't enjoy using this card and quickly went back to my old RB.