I personally find T-diagrams more time consuming than taking a few extra seconds to understand the actual question, i.e. I tend to rather read key premises again after seeing the answer choices when solving practice questions.
In a controlled environment (even if I time myself for every question, it's still psychologically different from a real exam experience), I agree that they are very useful in profoundly understanding a question's logic and learning how to trim the fat from the text and leave it to its bare minimum. However, I feel they are somewhat impractical.
What are your opinions on T-diagrams advocated by MGMAT? Are there any alternatives?
GMATPrep 1: 410 Q26 V20 (20 and 19 incorrect)
GMATPrep 2: 620 Q44 V32 (12 and 14 incorrect)
GMATPrep 3: 690 Q48 V37 (12 and 12 incorrect)
Most important lessons learned so far:
1) Your first prep is NOT indicative of your true level.
2) First 10 questions ARE important (notice that between preps 2 and 3 I had only 2 less incorrect questions on Quant, but a 70 point total score difference)