All the sims will allow you to use your own transmitter, even the ones which come with their own controller. All of the high end sims use some sort of hardware dongle which is required to be connected to the computer. In RealFlight the dongle is builtin to their controller, so to use your own controller you plug it into the RealFlight controller. The lower end sims like ClearView and FMS don't use dongles, so you just use a generic cable from your transmitter to the computer.