I was interested in buying a new transmitter combo, wondering how well each one works.....what the advantages are of one over the other??

Your question makes no sense so some clarification is needed. I have the futaba 3pm(2.4 fast) and love it. It has all the necessary features to compete with radios that are priced much higher. Never had a problem running any of my cars and as long as you get the 2.4 model you dont have to worry about glitching or interference.

If your question is: Is the 2.4 model better than the FM model....Yes
I would rock a losi 2.4 radio before i touched a FM transmitter again. No glitching and interference is well worth the price.