What is the difference now a days? Is it safer to go to one over the other? Is there going to be a bust on these things soon? Is there any less risk for a lady working at one over the other?
In 99% of the cases... I've never found any difference. The issue probably has more to do with getting a business licence from the city. But in recent years... I think they've caught on to the game and realize what's going on in "most"... but not all places.
I'm not a lawyer... but from my knowledge the answer to your question is yes. Also from my findings... not all the girls have certification but the manager or owner usually does.
Is it safe? That depends on your definition of safe. I don't think your neighbours in the apartment would enjoy clients visiting you at 11pm each night... so a lot would depend on how discreet you were. Is it legal? Obviously not if additional services were provided.