With all due respect to Gui's opinion, the type of system you are describing can be a practical solution for a lot of people who are looking for the convenience of a main furler and don't have the money to purchase a new furling mast, boom or retrofit system.
With some modifications to the goose neck, a few custom made parts for the mast head, some work on the boom, a system can be rigged for not much more than the cost of rigging a new headsail furler.
You most certainly will sacrifice performance. But many people find that a price they are willing to pay.
We're not all racers.
agree..good point...sorry I sounded offensive