Do you mean Mk 1 or Mk 2?
I think Tempest’s reply refers to a Mk 2.
The Mk 1 uses a genoa fitted with the conventional luff wire which is threaded into a split flexible plastic spar. On the Mk 1 inherited with my boat the top swivel was linked to, but seperated from, the forestay by a short S/S strut which kept spar and stay apart and prevented the halyard rotating as the genoa was rolled up. The spar is needed to ensure the genoa is rolled up evenly along its length. I found the Mk1 worked reasonably well but, because the spar was split, its torsional rigidity was not that great and the top of the sail tended to open out, reducing effectiveness and pointing ability. Doubtless compounded by the fact that my genoa was not cut as a reefing sail (needs to be flattter, to reduce the mid luff “bag”).
As I needed a new genoa anyway I invested in a Mk 2 in which a similar, but not split, flexible plastic spar is threaded through a luff sleeve (no wire). The fact that the spar is not split seems to make it torsionally much more rigid. Combined with a sail cut for the purpose I have found the Mk 2 to perform impressively and I am very pleased with it. How much of the improvement is because of the unsplit spar and how much the sail is difficult to know, but I suspect the spar is the more important.
I didn’t chose the Harken high load drum because I do not have a system for tensioning the halyard sufficiently powerful to require it. That is about to change and I am expecting to have the choice of releasing halyard tension before reefing (each time) or upgrading to the Harken system.
There has been a previous thread on this in the technical section which can be found by typing “helyar” into the search box.