The Lucky 13 suits Diminished Tuning perfectly because it gives you a full three-octave range - and my unique LOOK-DOTS on the front of the comb mean you will always be able to keep your place with a quick glance!
It is a symmetrical tuning (every hole has the draw reed one tone above the blow, the next hole always starts one semitone up, and every octave is the same). This means you can instantly transpose phrases into different keys and octaves, simply by moving them to different places on the harp.
That's particularly helpful for jazz improvisation, where rapid key modulation is essential to get around the chord changes. But Diminished is great for other styles too! As every draw note can be bent a semitone, it's very expressive for playing in any genre: Jazz, Folk, Pop, Country, Blues, Balkan, Middle Eastern... you name it.
Besides full chromaticism with simple draw bends, the big advantage of Diminished Tuning is that there are ONLY THREE PATTERNS TO LEARN for any scale or lick, in all 12 keys! That makes it way easier than any other diatonic harmonica tuning in existence to transpose your favourite phrases quickly to whatever key you want, without changing harps.
PHRASE MAPS help speed the process of learning, by giving a clear visual reinforcement to what's happening with the harp in your mouth. They simply involve making lines between cells in a tuning table, to indicate the path your mouth takes and the breath changes and bends involved. Because of its inherently symmetrical repeating structure Phrase Maps suit Diminished Tuning perfectly, and can help you master it quickly throughout the whole 3 octave range. Here are Phrase Maps of the three Major scale patterns that will allow you to play in all 12 keys on your Diminished harp (you can play along to me demonstrating these patterns in the VIDEO).
I hope that's whetted your appetite to try a Diminished Lucky 13 yourself! Even if you stick with your standard harp tuning for most playing, having a Lucky 13 Diminished harp in your arsenal will give you the ability to play tricky tunes and phrases that simply don't come easily on normal harps.