I see no reason to worry about it. We often run two at the same time.
I'm sure many lower quality/price restaurants often run several at the
same time. IIRC, unless you are standing VERY close to the microwave
AND it has a defective door you have nothing to worry about as far as
stray radiation. And it's not like it's stray x-rays, it's just radio
waves.

I agree that it's probably safe, but your argument here sucks.
1: The microwave frequency is specifically designed to cook meat.
If you happen to be living in the meat in question, cooking
it is clearly bad. You can do fairly significant long-term
dammage to yourself without becoming uncomfortable, by exposing
yourself to microwaves.

The good news is, the levels of such radiation that escape the
confines of a properly working microwave are so low that, with
the added defense of the inverse-square law, its's almost impossible
to get enough of them close enough together to do any damage.

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