What the manufacturer doesn't mention is the one great inherit drawback of cathode follower output stages. Cathode followers have less than unity gain, so 100% of the voltage swing must come exclusively from the small signal stages. Most any small signal stage's distortion spectrum will be weighted heavier towards high order harmonics than a DHT power triode using a "traditional" output transformer output coupled configuration. This is especially true for cascode stages, and other super high gain small signal stages capable of such large voltage swings. Even a voltage amplifier stage using highly linear, low mu small signal triodes cascaded together won't be low distortion any longer by the time it has to swing a few hundred volts. There's a good reason why cathode follower output stages aren't more popular.

Thermionic