I don’t have fcpx in front of m but if I make no mistake you can create an mp4 file using the “Apple device” setting. One of the submenus will give you the possibility to chose “Computer” and this creates a non .mov h264 file.
Could be a solution to your problem without goint to Compressor ?
Patrice Freymond
Editor  Certified Trainer FCPX 10.1.3
Post Consultant
Always learning…