I have the Mitsubishi Mr. Slim FD12NA mini split heat pump installed in my shop in PA. Fantastic, 23.0 SEER, 12.9 EER and 10.5 HSPF have had it one year and have to say we don't notice it on our electric bill - like keeping a light on. AC works great and heats with outside temp at -13 degrees and you get 100% of heating capacity at 5 degrees. No issues all winter and we had a colder than usual one here this year. I would think it would work great on an island where you will only use it May thru November. I will certainly consider it if we decide to go to an HVAC system for our island home - currently have hydronic electric baseboard heat, no AC. Here is a link to their catalog:
http://www.mitsubishicomfort.com/med...im_catalog.pdf