I like him, but not as a CM in a two holding-CMs formation. To play a one-footed player in that position is very risky!
I lost hope in Alena tbh but changing his positions is one of those risks that are interesting to see.
If you are putting it on paper, Alena has qualities that allow him to play this position, but irl it is different thing. Player change positions all the time, sometime it works and sometimes it sucks.
Thiago Motta started his career coming from B team as SS/AM, we turned him into defensive DM, and even used him a CB when needed (ironically it was against Benfica team coached by Koeman iirc)
Alena as CM, played very high on the field, loved to go to penalty areas and was overall closer to Rafinha than Motta. If he can be disciplined to keep his ground, be aggressive without the ball then he might be decent choice.
That being said, I won't be surprised if we sold him