I’m sure Ralph will comment (though he already offered information on the difference between the Zero Autoformer and the output transformers in tube amps just above---did you miss it?), but may I say that when you say "non electrostatic speakers" you are assuming ESL’s are a high impedance load. Yes, the original Quad (57) and other 50’s designs were nominally 16 ohm (though very, very low at some frequencies), but modern ones sure aren’t. The current Quads are at most an 8 ohm load, other brands often 4 ohm. So they too, though being electrostatic speakers, benefit from the Zero.
As to whether an OTL does or does not have any advantage with non-ESL speakers, there is more to that question that simply the matter of the presence or absence of an output transformer in any given amplifier. The Atma-Sphere amps have many other elements unique to their design than that.