The correct (first) question about iverify.vip is: "How many (what % of) providers in your area use it? "

 
Sadly, I do not have the answer, which suggests the percentage in my area (SFV) is low.  

 
Life is good

 
The Cat

I don’t rely on any site to verify potential clients.

The site you listed gathers information from providers who share information about their clients. They want providers to give detailed information & pay for a membership that’s wrong. I would not share any information without consent. I don’t use P411 as a verification site. The sites that state they verify are not doing criminal checks for our safety.