I think you're right to thank them for their difficult job. I seriously got bored just reading the description of your setup. What percent get through to the second email? Is it like 10%? 50%?
(1 per month + (1 per 6 months)/6) / (200 per month) = 0.58%.
The more important nugget is that he is contacted about two attractive opportunities a year for his passive method that have a fairly high probability of leading to offers if he is interested. This enables him to:
1. Accurately appraise his worth to companies,
2. Quickly scale to a much higher number of interesting opportunities through the 14 worthwhile recruiters per year that already value his conduct (even if only 2 per year have opportunities with appropriate fit) by actively involving their aid if he becomes dissatisfied with his current employer/role (or they become dissatisfied with him),
3. Identify hiring trends in his field.
I for one think it is a brilliant strategy, and I'll probably adopt it myself!
