Yep, although never did very much with complex analogue circuits, mostly digital stuff. Actually this baby seems quite complex for what it does. Nowadays one would probably do all the filtering and phase matching with some sort of microcontroller and some clever software. Like A/D-converter -> µC -> power stage, with off-the-hook components. Maybe with Raspberry Pi or such. Would be a fun software project I think, although lots of work.
I've done some trivial stuff with analogue, but I've mostly done digital stuff too (unsurprising given I'm a software person).
Agree - it is quite complex, given that it doesn't "do much". That said - I've done a bit of a 'literature review' of sustainer systems and the difference between a a dead-simple sustainer and a more complex system is essentially performance and features: harmonic mode and not having a SUSTAINER ACTIVATED speed hump. I gather the sustainiac and the Fernandes system are analogue to keep the cost down...
... for them, not us