I still see misinformed claims that transmitter kits are not allowed under the part 15 rules. Consider the facts.
A kit consists of parts and instructions for building a transmitter.
The part 15 rules allow individuals to build homemade transmitters.
What is a home made transmitter? It is a set of instructions, written by you or anyone else, describing how to build a transmitter from parts.
The kit makers provide the instructions and parts for building a homemade transmitter.
Case closed.