I've been struggling to memorize the entire guitar fretboard for several decades, and I blame the Germans! :-)

Context:

* in USA & Canada, notes are a-b-c-d-e-f-g

* Where I'm born though, due to Germanic tradition and influence, b is called h. b-flat is b.

* Given that most teachers start you with C major, it was taught as c-d-e-f-g-a-h

* And of course, where I'm born, you're first taught solfago (do-re-mi-fa-so-la-si/ti-do)

So my brain never really learned to think of musical notes as "alphabet". My natural inclination is solfago, and when I use the single letters, my brain interprets them as random string of letters that you have to think about every time (given that for whatever reason "H" is between "A" and "C"), rather than just alphabet. It's like I have two parallel sets of neural pathways: Alphabet - no problem, I can do it forward and backward reflexively, vs Musical Notes - stop all trains, engage upper brain functions, this is the difficult one with no sense or reason.

Grrr, Germans :=D

... that being said, I'll try the app :)