These in mast
furling (or in boom)systems work
ok at the high end of moderate conditions when you are only doing "cosmetic reefs". When you really to reef for a period of time in heavy air there is a tendancy for the leech of the sail to creep and power up the sail making beating difficult and causing excessive heeling. Slab reefing systems are a more effective and reliable method.
There other issues with in mast furling such as significant weight aloft from the heavier spar which decreases stability and increases rolling (an important consideration on a round bottom centerboard boat
like the boat in question.)In mast furling tends to shorten the lifespan of the sail. Also the hollow leech really kills light air performance.