The bad habit thing... I don't buy it.
The bad habit thing comes from experience. I self studied and got a great score that by most people's standards would make me a self-study success story.
Once I trained to be an instructor, it was like the fog lifted. I had been doing everything the hard way. I was using tick-tack-toe graphs for games, I had no understanding of the question types, and no recognition of or system for eliminating wrong answers. I spent hours beating my head against the wall with bad books and PrepTests while not really learning anything. I was completely relying on my own brain to analyze each question as if I'd never seen one like it before. After taking the actual test, I was exhausted.
Why was it like this? Because I was content getting high practice scores and wouldn't consider hiring someone to point out how I could do it all much more efficiently. The only feedback I got was from my preptest scores. On the real test I left points on the table that I didn't have to. I'm fully convinced that if I had taken a good class or hired a top-notch instructor, I would have scored higher, easier, and with less study-time and frustration along the way.