Sorry for using "CB amp" as a description,
It isn't a real specification anyway. I just meant a type of amplifier that was gererally of a simple design that doesn't have a lot of features. As Alison says, e.g. the EB63 uses basic diode biasing which needs high current in order to maintain a stable bias. This results in low efficiency and higher battery drain.
Such types might also might be considered a single band design, as there is often only one (or none) lowpass filter. They also generally have no gain compensation, which means uneven power output has you change bands, which would require transmitter power adjustment to keep from overdriving and burning out the final transistors which are not cheap.
The latter point really makes it not a good match for the ubitx since the transciever already has quite uneven power ouput with good power on the low bands and less and less as you go up. An uncompensated amplifier will also do the same thing so that can be a troublesome thing to handle.
The AN763 would be a better match up as it has gain compensation built into the design already (no need to figure it out on your own, or extra parts to buy). It also has a more efficient design for both biasing and for the final transformer (less heat and lower current draw).
Alison, I don't quite get what you said about the copper heat spreader and the AN762? Reading the construction notes for both the EB63 and the AN763, I couldn't find a mention of that, or that the AN763 would have any more rare parts than the EB63? Both seemed to be complete kits that only required a large aluminum heatsink and a heatsink fan (besides a case and lowpass filters and switches).