Ive seen plenty of Steez's / Exists (whatever the pluralism for many of them is) and other's like Stella's and baitcasters made of Mg that have corrosion - one was a corker naturally second hand and sold as excellent condition ��
Having said that they're marketed by Daiwa as "salt water safe" - so are many things denoted as "safe" for example walking down the road, eating sugar and argueing on the internet. Mg is going to naturally act like an aspro near saltwater (
https://m.youtube.com/watch?v=1thsAwgSd5U) especially if the surface treatment has been breached - then you'll get these weird paint subterranean creeping lines from that point and then the Mg going like Aluminium affected by Gallium.
Best course of action is care - wash and oil it with a good lanolin based oil and dont be shy with it. Paint under the cowels with a marine grease and or lanolin grease so that water sheds off the body under these areas that see little air movement and overall care.
While a great reel to own and use - its just a worry that you will eventually get Mg cancer / corrosion if your not careful. I own a couple of Mg reels myself - yeh their days of saltwater use are over / never occured a long long long time ago.
Thats my honest opinion.