Not OP but I have extensive experience with it. I used it often in college (10+ years ago), both with and without theanine and other similar substances in my stack. The effects were noticeable and much less jittery than from nicotine.
Positive: My working memory felt faster and less error-prone. I've always been good at mental math. Speed is my strength but I make lots of mistakes and things sometimes seem to "pop" out of my WM against my will. This seemed to (qualitatively) happen less often. I remember that I had some quantitative metrics on two-digit by two-digit multiplication that showed positive results, but the data is long lost to time.
Negative: Mild to strong nausea and light-headedness. It often felt like I had vaped too much. This was never bad enough to negate the positive effects.
Overall I think it's a useful performance enhancer for time-sensitive intellectual work, but I'm afraid it may be too strong for daily use. You will see rapid desensitization if using more than sporadically.
Positive: My working memory felt faster and less error-prone. I've always been good at mental math. Speed is my strength but I make lots of mistakes and things sometimes seem to "pop" out of my WM against my will. This seemed to (qualitatively) happen less often. I remember that I had some quantitative metrics on two-digit by two-digit multiplication that showed positive results, but the data is long lost to time.
Negative: Mild to strong nausea and light-headedness. It often felt like I had vaped too much. This was never bad enough to negate the positive effects.
Overall I think it's a useful performance enhancer for time-sensitive intellectual work, but I'm afraid it may be too strong for daily use. You will see rapid desensitization if using more than sporadically.