A suggestion for the upcoming products would be to change the display from numbers to maybe something a little bit more modern. For eg a 4-line led that gives a bit more information, such as TITLE (eg MindLearn), duration, target waves. Think of mp3 type players and then port the same type of idea to this.
Another idea is a pause button, sometimes we may be doing something. Eg studying and then someone will interrupt us. We don't want to replay the whole entire session, and we don't want to miss out on the section we are up to when the interruption occurs. (eg phone call), it is something small but distracts us and also requires us to take the headphones off. Maybe even implement something that has a rollback feature, for example when you pause and then you replay the replay starts from a minute before you paused it to retrain you into the rhythm you are in. EG you pause at 11 mins. Then when you replay it is starts at 10 mins and you repeat the 10-11 part to kind of remind your brain where you are at.