Anything apart from the two mainstream default harmonicas (Solo-tuned fully-valved chromatic, and un-valved Richter 10-hole diatonic). Alternate tunings, different construction, new functionality, interesting old designs, wishful-thinking... whatever!
I just received this yesterday. I've tried the circular kinds but I like this linear layout much better. Made of thick, sturdy plastic. 2-sided with tons of information. Dead simple to use. Wish I had this years ago.
