In addition to what Don mentioned, it's more ruggedized in it's construction.
What I am happy about is the higher IPX rating and 1 Watt speaker. The FT3DR is IPX5, while the FT5DR will be IPX7.
If my understanding of the IP ratings is correct, the FT5DR should be rated for submersion between 15cm to 1m for a maximum of 30 minutes.
1 Watt speaker will be nice as well in noisy areas.
