Privats are hit and miss, firstly there english is lacking so it is hard to negotiate, also they are normally further out of town.
As for there safety, alot of them are safe as they are run by maybe 3 - 4 woman who have decided to rather open there own place of business than to schelp themeleves into a club, then theres the issue with discrection, it is alot more discreet to work in a privat, as they dont have to worry about bumping into anyone that they may work with during a day job.
The ones that arent safe, normally have girls stand around and then lure you into them with promises of cheap sex, these are operated by there pimps and there friends, and can get ruff if you decide to try and contest the disgustingly high bill you'll get.
Best thing to do is to go with a couple people, when you have a few people with you then it is alot easier as they do not tend to pick on groups, only single tourists that happen to be stumbling about on there own.
And as far as health goes, well it is up to you to judge, check to see if they have showers ask if the girls shower after every client, make sure they use condoms, ask if you can bring your own condoms, make note of the cleanliness of the rooms make sure the towles are clean, the list of things to look for is endless.
Hope this helps
Cheers
EuroLover