"Yellow Letter" Campaign successes in CA??

I’m in transition from Realtor to Investor and live in North CA. Wondering if there are any Ron LeGrand students out there who have successfully used the Yellow Letter marketing method. My LeGrand material is a little outdated, but getting ready to spend some $$ on marketing and have some questions/comments about the method. Sure would love to hear from some of you that believe it really is “the most successful method of mailing” out there, according to LeGrand and others. Even if you are in another state or market, please post and
Thank-you for your feedback.