Autoblock is easily tied from a loop of accessory cord: just wrap
the loop around the standing line several times, and clip the
ends with a locking carabiner. It also works when tied with 9/16"-in
Spectra® webbing (I suggest trying it with about 5 wraps to
start). Many climbers use this knot as a rappel safety, a practice
that I don't follow for a variety of reasons. The knot can be released
under load by pushing down on the top coils. As an ascender knot,
I find it works well, but one must pay attention to the coils
to make sure that they don't cross. This can be avoided if the
sling length is carefully chosen, but normally one ties this knot
with whatever sling is handy - I've even seen people use a sling
that still had a hexentric on it because it was the only one available!
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.