Thanks all of you for your interesting and helpful contributions. Great to get a spread of ideas, impressions, suggestions.
On a personal note I think I should clarify something. I created the SlipSlider as a (hopefully) useful harmonica for the biggest group of harmonica players: those who play unvalved diatonics. The vast majority of them use Richter tuning, but the SlipSlider can be adapted for other tunings like PowerDraw, PowerBender and many more.
Unvalved harmonicas allow overbending - which has gained a lot of traction in recent decades because it's been the only practical way to retain the traditional sound/tone of the diatonic harp and achieve full chromaticism. However it requires hand customised harps to work properly, plus many years of practice to do it well. And the sound and pitch of the overbends is not always good to many peoples' ears.
The SlipSlider gives diatonic harp players a new alternative. The accomplished ones can continue to use all their hard-won overbending skills, and add new bends as alternative notes or for expression. Those who struggle with overbends, or just don't like them, now have a new way to get full chromaticism without compromising on the traditional unvalved sound and tone they love.
All good, and I hope it's well received by the players it's designed for over time. As for me personally, though I'm enjoying exploring the SlipSlider, I was never anti-valve. Most of my harps are half-valved and the ones that aren't are x-reed harps like the quad-reed AsiaBend, UniBender, XB40, or triple-reed types (mostly SUB30 customs in PowerBender tunings).
My heart is more with developing the x-reed direction for my own playing. I know that's likely to remain a niche area in the general harmonica field, but to me it's the most interesting and exciting. I also think half-valved chromatics are the current best option for easy chromaticism with bending expression - they're my choice anyway, and have been for a long time.
But... All these harps (except the AsiaBend) require valves, and the vast majority of players don't like valves at all. Fair enough: they do alter the sound of the harp, and can cause trouble (though very rarely with half-valving). Even though I don't play unvalved harps normally myself, it's an interesting challenge to think of ways to enhance the capabilities of such harps for the big majority who do.
The SlipSlider is one of those ways. I think it's a good one, but clearly it's not as simple a no-brainer to adapt to as I first thought! I have some other approaches along similar lines in the pipeline, and will soon release a simple idea that should be easy for any harp player to use. Happily it can work in conjunction with the SlipSlider to add a double whammy of extra punch to the humble 10-hole diatonic