ZOTL actually has nothing to do with traditional OTL beyond similar acronym. Traditional OTL paralleled numerous tubes to reduce output impedance. ZOTL uses 4 output tubes for 90 watts and performs its magic completely differently.
So, prejudge based on anonymous IMHO's
or listen for yourself http://milbert.com/show/201206NYAmpShow
GAGA, whose underlying tech is particularly well regarded for superior bass amplification using tubes, was also recently used on entire Blues Gypsys album, with none of the "tone and behaviour ... constantly changing, rendering it utterly useless in recording." LOL