Sorry to be “that guy” but can’t seem to update my profile picture. Just a heads up. Love the idea! And the UI is super nice. Just posted a reflection.
I purchased the powder on amazon (Nutricost L-Theanine Powder). It comes with a 200MG scoop and I just mix that into my cup of coffee. For me, it lasts around 2 -3 hours, doesn't impact the taste, and eliminates the jitters that I receive from caffeine.