As a point of reference, my present amps are 300b parallel SET, so the LTA amps were compared to those.
I found the ZOTL40 preferable in my system according to my likes, which skew toward three dimensional midrange emphasis, while still offering excellent treble extension and bass control. It had more meat on the bones than did the Ultralinear amp, which I found rather clinical...again with perspective on what I presently own and have enjoyed for over a decade. Both LTA amps produced better bass transparency (neutral and defined) than the 300b parallel SET amps. I think one aspect of 300b bass reproduction I enjoy is a tendency to skew toward warm fullness and away from absolute accuracy. Still, the 300b parallel SET amps reproduce acoustic string bass bass with exceptional detail... vibrating strings can clearly be heard. The ZOTL40 offered more warmth than the Ultralinear, however bass was not bloated whatsoever.
Ultimately, neither LTA amp offered enough difference, or “improvement” (in quotes because of the completely subjective nature of the word) to cause me to keep them. The fact that I require mono blocks for my system configuration made switching to LTA amplifiers somewhat cost prohibitive. It’d have been a different story if I required a stereo amp.
Another amp I recently tried and really liked were Atma-Sphere M60 OTL monos. Those amps convey most of the attributes I love about the 300b amplifiers while offering bass control and transparency akin to LTA amps, which makes sense considering both are OTL. Those of you who like LTA amps might enjoy auditioning Atma-Sphere M60 amps (or a stereo S30) on your Spatial Audio loudspeakers.
LTA builds excellent amplifiers. I understand why many people love them.