No one has ever recommended using galvanized steel wire to wire trees, lol!
I tried using galvanized steel for tie downs and guy wires last season because all the cool kids were doing it. Galvanized steel is not stainless steel, so it will rust and corrode when kept wet. I actually helped repot a tree that was purchased from Mirai, and the galvanized steel completely disintegrated after approx. 5 years in the pot. There was nothing holding the tree in at all!!! On the bottom of anderson flats, the galvanized steel rusted and snapped in as little as one season! On the bottom of regular pots where there is airflow, it has held up well over the past year. However, it will leave rust marks on the bottom of your nicer pots.
Its great for guy wires because the 18 gauge galvanized steel is stronger than 18 gauge copper. However, I have decided to stop using it for tie downs once my roll runs out, and switch back to aluminum. Aluminum is more brittle, but will last a lot longer since it wont rust. I have also noticed a big difference in between Japanese aluminum bonsai rolls and American. Its worth the extra money for the real Japanese aluminum wire, hands down!