Match betting is not 100% illegal, however many crypto casinos/sportsbook might accuse you fraud, void the bet and you will have problems when withdrawing the money.
Soon or later the crypto casino/sportsbook will know when you place a "Free Bet" on casino A then you place a "Lay Bet" on other casino.

And when there is an issue with your account because of the matched betting, not all crypto casino will return your deposit/free bet and not all crypto casinos allowed Italian users to play on their platform (depend on the casino license).
Im not saying that matched betting is a crime and you will get trouble with crypto casinos, its just a friendly reminder so you must research more about crypto casino first before doing that.