Look at the specs. The H version comes with a bigger (1000mah vice 600) reciever battery and 3004 ball bearing servos vice the standard 3001 servos.

The swithes are different slighly and the throttle ratchet.

If your planning on flying heli's at some point get the H version, planes fly just fine with a smooth throttle.

You don't need a syth unless you want to channel hop, if you get a syth rx there's no point unless you get the synth transmitter module.