Isolation Transformer Safety
The transformer will be "safer" than the same voltage direct from mains as it will not be ground referenced.

Note that 200VAC + is lethally dangerous if you touch it. Even with dry hands and no earth if you make two point body contact to any body points across 200VAC+ you MAY die. I have had probably dozens of 230 VAC shocks across quite a long lifetime  - and while some were quite nasty I was in all cases 'lucky'. For some people the very first is fatal.

Note that if you ground ANY one point of your isolated output circuit then the isolation effect is wholly lost.

What sort of power supplies do you have in mind that need 210 VAC? MUCH lower voltages are MUCH safer. Use 210VAC only if essential.