No offense taken- but as an instructor, I am trained to take beginners. Tech divers are not.
The tech diver in question may have done just as good a job as me... or not. As this thread isn't part of the Accident section, we can assume he lived- like the vast majority of first-time divers. But as a 'general practice' I would suggest that laymen are not the best diving instructors.
You can learn to drive a car with an experienced driver, or a professional driving instructor. One is free and one is not. If asked which would be safer, I would answer the pro. If asked which one would lead to a better beginner driver, I would again choose the pro.
Respectfully, I think that's a load of crap.
I learned to drive a car from my dad in a parking lot... In the 27 years I've been driving, I haven't been in an accident, or had a traffic violation of any kind.
So...
Let me say this... I'm not implying that you aren't a good instructor. Frankly, I don't know, and am not qualified to comment on that.
At the same time, there are plenty of instructors that have way less experience than me, or others whom I know, and I'm pretty darn sure that without me being a "professional" instructor, I would venture a guess that I could give someone a way more comprehensive scuba education than let's say the guy who has 200 dives... regardless of how much they paid to become an instructor and they were taught some approved method for teaching.
Again... I'm not saying that all instructors suck, and that I'm great. What I am saying is that just because someone is a "professional instructor" doesn't mean they're going to do a better job than a layperson with a lot of experience.
As I stated earlier... The instructors will all say, "use a professional instructor" and quite frankly, to get someone certified, you have no choice... But if I was going to take a friend of mine who wasn't certified, on a shore dive here in Ft. Lauderdale (where the maximum depth is 15') with my equipment, I wouldn't think I was doing them an injustice. YMMV.
Think about this... If I give my friend a DSD class, then they may actually WANT to get certified, and be great at it. It's hard to make a $300+ commitment to something you might not even like at all.