I just went through this process. I did a fair amount of research on different furling units and spoke with lots of people. Came down to the "popular" choice of Harken III, unit 1. I also decided to have a new 145 triradial genoa made for the unit by Doyle. (I was more concerned about cruising and PHRF than one design. Also wanted to reduce power a bit since I don't have a lot of "railmeat" in my normal crew.) It has a higher cut clew so you can see under it. I had older class sails from Haarstick with hanks. You need to have lufftape if you don't already and you will likely need to cut down your class sails to work with the furling unit. It is a combination of the "airblock" at top of halyard and the height of the drum off the deck. You can take the drum off but you may have to take off airblock or use #2 halyard to hoist other non-furling sails. Removing the airblock would require disconnecting forestay. Not something you will likely want to do! Also you need to know that forestay will need to be shortened (cut) for Harken unit. My existing one was in good shape so I kept it as a spare and had a new one made. I will tell you that the unit works great and it is much less wear and tear than getting up on the foredeck to change sails! The only downside is that the units are pretty expensive. If you can find a good used one, I would go for it. But also assume you will have to save some $ to modify your sails. Hope this helps.
