I have purchased David Lindahl home study course, attended seminar and am a former student of his coaching program.
Generally speaking he knows his stuff and is one of the few real estate investors that I know of that buys and sells apartment buildings in the current market place. I found his books and material to be a good resource. His information appeared to me to be in real time and not techniques that were outdated.
I have lots to learn, but getting started it helped me begin understanding the apartment business. Any successful business person always wants to make more money. David Lindahl has been able to capitalize on his niche and sell other products.
Summary, you have to take the good and bad and apply to your situation. With any course, program, free seminar, etc. it is up to you to take what is presented and take action. Someone already said "take action and I completely agree.