The problem is terms like "controlled by a pimp" have very broad meanings. Any escort who works through an "agency" (incall or outcall) could be deemed "controlled by a pimp" (i.e., the agency's owner or management).
I.e., if you call an agency, and the agency sets up a "date" for you (tells her where to be, when to be there, and what the rate is) then the agency could be considered "controlling" the girl "for another person's gain".
And going with "independents" isn't without risk either. Just think of the situation in Toronto with many EEs and Asian "independents". They may be here on their own volition but chances are they also have "pimps", who might have arranged for their visas, flights, holding their passports, etc.
If caught in a sting, suppose the girl "claims" she was forced by her pimp (even if she wasn't) to avoid prosecution by becoming "the victim". Then you the John are looking not only at a prostitution charge, but also a RAPE charge!
You can't even claim that you didn't know. According to the article, "pleading ignorance of the circumstances under which a prostitute is working will not count as a defence."
The cops will simply say, "you should have known," and will throw the book at you.
So even with independents, how can you be 100% sure the girl doesn't "have a pimp" and wont "claim to be forced" if caught? You can't... and thus the risk becomes astronomical considering the possible criminal charges.
Even if you pay money to the college girl who lives next door, whom you've known for years, whom you thought 100% sure was doing this on her own... she might later claim her boyfriend made her do tricks for money, and you should have known she wouldn't have sex with you for money unless under severe duress.
Now suddenly you're looking at serious jail time.
Of course we wont know the real effects until such a law is passed. But while such a law appears to well intended, I'm afraid it will just drive prostitution solidly underground, and the girls who are most vulnerable will be even farther away from help.