I have a spinnaker halyard which I imagine can be used at the mast.
yeah.... in my experience, the top-down furlers work best when the furling cable (the "anti-torsion" cable) is loaded up enough to be effectively straight. May not be an issue in light airs, but if the cable can bend appreciably, it can make it so the system doesn't cleanly furl the sail (it may bunch up and/or not smoothly furl). It's a problem we don't generally have with traditional rotating-headfoil furlers
So when you're sizing things up, make sure you're considering the amount of load you'll need to be able to apply at top and bottom (tack fitting, spinnaker halyard) to be able to ensure it works smoothly.