I was the student of Dev Sir for two years while preparing for IIT JEE in my class 11th and 12th.
The main quality of his teaching is to focus on developing thinking ability rather than just giving the concepts to solve problems which really goes a long way.
In those two years, I developed not only the math skills required for competition but also my reasoning and thinking skills improved a lot.
At times we were not that motivated or felt overconfident, he also provided a reality check at those times.
You could reach him in work hours for any time (when he isn’t taking classes) for any doubts you have.
I graduated from NIT Warangal and currently working as a Software Engineer at Oracle India Development Centre.