It's totally doable. I dive my Fusion year round here in SoCal. I've even taken it up to the colder waters of NorCal (48 degrees F). With heavier undergarments (400g thinsulate), I can pretty much go 4 dives in a day without getting cold. My husband and I also just got back from a trip to Roatan (79 degrees F). We both brought our Fusions (my primary suit, his back up suit) and we were SO happy we did. Obviously we brought much lighter undergarments...and though we did get some funny looks from all the divers, we never got hot and never got cold. While the other wetsuit divers in Roatan were doubling up their wetsuits because they eventually got cold, my husband and I were perfectly happy with our drysuits.
I love my Fusion. Though, it wouldn't be a bad idea to do as Bubbletrubble says and test it out before making the purchase.