I came across this case of a voyeur who placed phone cameras under the sink in a toilet. Note that this did not even make BBC news - this is on a local London website.
Women secretly recorded by south east London voyeur | This Is Local London
This was a toilet in a hairdresser, so not open to passers by and with the need to make a booking to enter the premises. So it would seem to be a low-risk environment. But unfortunately this did not prevent an employee from committing a crime. While the article is not clear that the toilet was unisex, presumably the offender was able to enter the toilet and place the phones inside because he was using it himself and was therefore unlikely to be challenged.
In my opinion this case suggests that unisex toilets, even those which are in what we could consider to be a relatively 'safe' environment, present greater risk than toilets separated by sex.