I use a Profurl Spinex for my downwind
asymmetric and upwind
gennaker. The advantage of the Spinex "balls" is that the diameter when you start to furl the sail is much larger than the diameter of the torsion
rope which makes it easier and quicker to start the furl - you have more leverage. Also the Profurl top and bottom swivels are detachable so you can move one set of furling kit between two
sails - maybe this is the case for other manufacturers as well.
Furling the asymmetric is a tougher physical job than furling the
gennaker due to the much larger sail area - 177 sg metres vs 116 sq metres. I still prefer the top down furler to using a sock or nothing. I tack the asym down to a hard point on the bowsprit which is attached through to the
hull. The top down furler works best with a lot of tension in the furler and I'm also nervous about lateral loads on the bowsprit proper. The separation between the tack point and the
jib furler is about 1 foot - which seems enough in practice.