Not safe otherwise
I don't like microwaves for warming bottles because its too easy for you to overheat the milk & burn babies mouth.
The only effective way to judge how hot it got is to stick your finger in it. Yuck! microwaves won't make baby glow in the dark or get sick. Babies don't need warmed milk anyway, if you set out a night bottle early & let it warm to room temp that's fine & some like it cold..