If you are considering changes, I wish lessons duration was more variable, especially when starting or doing custom character groups. My brain seems to be able to keep up for 30 seconds, not a minute. Options for early lesson lengths of 30 and 45 seconds would allow me to progress more confidently. I realize I can just use what is there until I can go a full minute, but it's frustrating when I get greater than 95% of the characters sent during the first 30 seconds, then about 40% during the last 30 seconds. At my age, 59, I find it difficult to develop my ear.
BTW, this is a great service you offer. Wish I would have found it 10 years ago.
That's only from TWO days work though - if you stick with it you'll find a different more "automatic" mechanism of decoding slowly develops . .