I don't doubt that this is the way to find a good recruiter. However, if I am going to put in the time to vet multiple recruiters in order to find one worth working with, why would I not just spend that time finding a job?
I work with about 70 companies (only in NYC) from pre-launch to almost IPO and a new role opens up to a us every week. It's helpful to find a recruiter who knows you & the market well enough to curate jobs you want and tell you about opportunities that might not even be listed or on your radar.