I got Telles in my WL rewards and used him in every WL (I'm a gold 2/3 player) since then, apart from a short intermezzo of Ferland Mendy TOTS (who was slightly better but imo not worth the 500k and having a red Telles on the bench), overall I already used him in more than 100 games.
How should I start, Telles is a decent player which is very strong on the ball and is key for my build up game. His crosses and through balls are amazing and he let's shine the winger in front of him. Also at corners he's a beast in 142 games he has 19 assists most of them come from corners he probably could have more but during WL I advise my fullbacks to stay in the back.
For me the biggest problem with him (this was also the reason why I benched him when Mendy Tots came out) is his lack of strength / physicality. He really struggles when he comes up against wingers like M'bappe and gets pushed off the ball to easy sometimes. Second minus for me is his pace, I know 94 is not really something you could call slow but in times of TOTS almost every winger has 98/99 pace or at least 99 acceleration (he has "only" 92) he really loses to much duels due to the lack of pace.
In a nutshell you get a really decent for 250k I stared using him again out of budget reasons because he's not so bad that it would make sense to spend 500k for a better option.
Dribbling / Strong on the ball and very good at passing and crossing as well as taking corners.
Often wins headers
Often looses duels versus strong wingers such as M'bappe due to his lack of physicality
Can be to slow when your opponent has TOTS wingers with 99 pace.