Anyone been in a "prostitute-only" open relationship?

I know open relationships aren't for everyone (and to each their own) but I often read people in them say that open relationships are difficult and require lots of communication (makes sense).

However, it would seem that one important reason they are difficult is that someone might develop feelings outside of the relationship. (This is similar thinking about why cheating hurts).

With a prostitute however, for all intents and purposes, that danger is removed. It would "seem" that if you were the open relationship type, that the removal of danger of your partner leaving you for someone else is pretty attractive overall.

I'm surprised I've never heard of open relationships where the openness only extended to totally emotionless sex (Where prostitutes (assume its legal where I'm asking this question) qualify).