The Hertz Donut mk2 was one of my favorite oscillators. When the mk3 was announced, I was intrigued by some of the new features but even more skeptical of messing with perfection.
The magic of the HDmk2 was that its raw oscillators had a sort of sparkly/dusty digital character, just on the edge of lo-fi. That combined really well with a clean and very easy to use implementation of TZFM. The structure was classic “complex oscillator” with a single mod bus — simple to use despite the name.
In comparison, the mk3’s raw oscillators are sterile and bland. But its magic is giving you a whole spice rack to kick things up a notch. You can make it sound a lot like the mk2, or like Noise Engineering’s bright and sharp-edged oscillators, or some synths of the 80s or early 90s, or lots of other things besides.
I thought the waveshapers (three of them, simultaneous, independent, and good) would be the main advantage over the mk2 (one shaper with three modes, all ugly). But having a third FM operator and a flexible routing matrix/bus hybrid, is golden. Monitoring Main and Op A in stereo while Op B modulates them both is an experience.
There are things I could be picky about — like having 6 styles of knobs where three would be fine — but honestly none of it poops the party. I think I might have a new favorite oscillator.