My Bristol 31.1 (currently for sale) has a Hood Sto-Boom, which I understand to be the original in-boom furler. There were many problems with this unit when it came out in the mid-80s, mostly because users did not follow the directions to have the aft end of the boom a few degrees up from parallell in order to assure that the luff of the sail furled properly. I have found that when the boom is set properly for furling, it works quite well.

I also crewed on the delivery of a 48' yacht with a three year old Lesure Furl boom. On a calm night in the Atlantic off South Carolina, the clew of the sail suddenly parted company with the boom. Even in 5 knots of wind, it was surprisingly hard to retrieve the sail. It turned out that the problem was caused by the sailmaker attaching the clew to the furling hardware with a piece of small line, which chaffed and parted. I don't know what Leisure Furl specifies for the installation, but if you have to use small line, you should certainly check and/or replace it regularly.

In short, they are not without problems, but when they work, they do make mainsail handling easier.