Spektrum is the only brand that authentically has the DSM2/DSMX protocol. They are vigilant in keeping it for themselves. In the past JR Propo used it but under licence. When JR Propo parted ways from Horizon, they switched protocols. Major Chinese brands, such as FrSky, have their own protocol which is different from DSM.

Another concern may be the programming language. If you are looking at a transmitter that is using the OpenTX open-source operating system, the method of programming is completely different from that used by Spektrum.

Allan