I’ve owned a number of amps over the years across push-pull, Class A, SET, and OTL. The OTLs I’ve owned are the Atma-Sphere MA-1 and the S-30, the latter of which I still own today and use in my second system.
In my experience, with the right tubes and the right speaker matching, an OTL amp can be endgame. The lack of output transformers provide, simply, just more music compared to any other amp type out there except for ultra high end solid state (like in the ~$20k+ range). But there are always limitations.
In order to be dynamic, most OTLs require a speaker that doesn’t dip lower than 6-8 ohms anywhere in its impedance curves. If the OTL is more that 100wpc, a speaker can dip lower, but at that point you’re also then using an OTL with a heck of a lot of tubes, and that means a bit more noise.
The best I’ve heard an OTL perform is to handle the mids and treble of a bi-amped Oris horn setup. Most high efficiency drivers are a match made in heaven when paired with OTLs, and being able to drive the bass sections with higher wattage and higher current amps enable the speed and punch that an OTL would generally sag.
With electrostats, it’s the other way around. The impedance curves dip in the treble, and the bass is easier to drive. If you don’t have enough power and current, using an OTL on electrostats will sound closed in and boomy. But with the right pairing, say the MA-1 with a pair of Quad, is another incredible match.
With this in mind, it’s been near impossible for me to settle with one amp, so I absolutely love my T+A HV stack in my primary system while still believing I will always own my Atma-Sphere S-30 even if I ever decide to consolidate my second system.