I almost bought a Rocketbox in kit form myself.
So I have not owned one.
Sadly due to ignorance I do not know if the amp is poorly designed and FET designs all work as advertised.
In general I like external amplifiers that use output transistors intended for the production of RF and I do not really care if they are bipolar, FET, LDMOS or anything else.
You really are best keeping them at stock output power and making sure you have a FANTASTIC swr and that the box's input and output tune are spot on. To put it bluntly there only redeeming quality is that they are insanely CHEAP !