Quite a few cavers believe that the Helical Knot is superior to the Prusik Knot. I find that it is easier to move when properly adjusted, but it takes some experience to determine how tight to make the knot. It appears to be more tolerant of excess slack than the French Prusik. Bob Thrun notes that most of the load is taken by the top of the knot, and recommends tying the knot by winding the free end downward as shown - but he notes that others have reached the opposite conclusion. I never seem to pay much attention to it myself.
The helical elongates more than the Prusik
Knot, but not as much as the French
Prusik. I've had good luck with it over the years, but I always
know that I have the Prusik to fall
The performance of any ascending knot depends on the diameter, material, construction, and condition of both the main line and the ascender knot sling material. It may also depend on exactly how one ties the knot. Your knot's performance can easily differ from mine.