I've also heard the single sided briefly at a private meet. Overall they have a very similar tonality. The double sided just seems a bit more technical and airy in the top end with a bit less warmth. Also powering the single sided was a bit more challenging to get its full performance since it's a few db less sensitive. We ended up pairing it with a Soncoz SGP1 power amp fed with a Ferrum Oor as pre which really seemed to bring them alive. Other lower power/gain headphone amps often maxed out before reaching good listening levels (Questyle CMA15, Topping DX9, DCS Lina for example - tested with my DS pair ).Have you heard the single-sided version as well? If so, I would really love to hear your thoughts on how they compare. I recently got to very briefly demo the single-sided and loved it. But knowing the double-sided is coming has prevented me from pulling the trigger...
So overall I'd recommend the double sided to people that wanna use them on high power headphone amps and are wanting to trade some warmth for some more technical performance. For single sided a speaker amp might be the way to go or a very high voltage headphone amp. I've tried the Violectric HPA V550 for example, which has plenty of gain for both. Topping A70 Pro worked as well but I'm not the biggest fan of the Topping sound overall.
Since the driver is so unusual in being low sensitivity paired with high impedance (my DS pair is 155 Ohm for example) it has a very unusual requirement concerning voltage and current and it's very hard to predict how an amp will handle this load without trying it out. But once you find the right pairing they reward you with a sound that rivals or beats headphones that cost thousands more imo. They might not beat other flagships in specific characteristics but for me they deliver some of the most balanced sound I've yet heard in a headphone. They kinda just get out of the way and just let you enjoy the music to the fullest without missing anything.
Btw. my absolute favorite amp I've tried with my DS pair was the Mass Kobo 465. But that is a 17k$ headphone amp unfortunately
But it shows that they have plenty of potential to scale with the source equipment used.