There are alternatives to the Prussik such as the Klemheist which don't jam as badly.
I wouldn't use a ring bend - the double fisherman's is superior for tying rope or cord ends together to create a sling. And I definitely wouldn't use either a ring bend or a double fisherman's to link ropes for abseil. An overhand tied in both ropes (with a 50cm tail) -aka the EDK or European Death Knot is way superior, as the body of the knot sits to one side of the line of the tightened rope, so it tends not to catch in cracks.
Finally, extending slings by linking them over and under into a reef knot is stronger than a girth hitch.
And I'd also opt for a Kleimheist or Autoblock over the classic Prusik.
Not sure if I think this was a good selection of essential climbing knots and the presentation was odd. For instance, I'd present the Prusik in an abseiling context. The article mentions using a Prusik to ascend their rope when they've fallen off an overhang, and I have yet to see that. What I see routinely is someone using a Prusik of some sort as a backup when abseiling.
But don't go climbing outdoors if you don't have someone that is experienced to go along with you. Take a course or several. It is possible to learn on your own, but it is a high-risk activity to figure these things out as you go on your own. Accidents, even fatal ones, happen to people that know what they are doing.
I carry a couple of prussik loops primarily for abseil backup, but have also used it to recover from a fall off an overhang when seconding. The leader was far enough away they couldn't hear me asking to be lowered. I also couldn't reach the rock so had to ascend the rope. Prussik gets the job done.
Fair point re: the Klemheist although the Prussik serves well enough.
For my part I wouldn't use a figure 8 in a bight to get a loop in the middle of a lonf rope that's going to take load - the butterfly knot is far superior.
IIRC the 8 on a bight is best for load parallel to the rope, and the butterfly best for load perpendicular to the rope. The butterfly is really fun to tie though :)
It's easier to untie. Has a cool method of tying. When a loop is loaded the knot becomes a bend. The alpine butterfly forms a secure bend, while the flat figure 8 can capsize at low loads.
I would use either for a directional load, but only an alpine butterfly if loading the loop is conceivable. And using the flat 8 as a bend is suicidal.
I'm a bit confused though, I thought you were referring to a figure 8 on a bight which is often used when cleaning an anchor while roessland seems to talk about using a figure 8 to join two ropes (not tying it on a bight).
Used the klemheist when I did rapelling to lock the break if I took my hands of the break. Preferred it over the Prussik as it bite better to the rope when under load because it twisted around it, and did release easily when the load was removed. It also was easy to slide along the rope.
From the time of your reply I assume you're also in Europe or at least not in the Americas. You are spot on in your guess. Colleagues and friends over the pond don't use the EDK for abseiling or rappelling as they say.
Also, not sure how the name was picked-up, but that's just plain bad marketing putting Death in the name :)
(Big caveat: this all depends on joining nylon ropes of similar diameters. Different diameters and UHMWPE cord has different rules)
My understanding is that the American's picked it up from the Europeans in the 90's, but then mixed up with the figure-8 knot which is the actual death knot. Some guy on the internet did some tests, and the figure 8 will roll and capsize at about 1-2 kN. Rappel loads are usually a bit under 1 kN, but if you hit enough snags, it could come out and there was a bunch of accidents resulting from that.
The overhand knot, when tied normally will role at about 3-4 kN which is well above a normal amount of force in a rappel. Also, it tightens as it rolls, so with enough tail, you'll be dead from something else before it could be a concern.
Incidentally, the double fisherman has a bad habit of getting stuck, so if you're doing multiple rappels, especially in icy conditions, or in sticky/jagged rocks, it presents a whole different safety problem.
Everyone I've run into here(Colorado) with more than ~2 years of climbing experience uses the EDK for tying two ropes together for rappelling. Maybe it doesn't come up in conversation as commonly since we typically use single ropes(as opposed to half ropes that you see a lot in the UK).
The etymology behind the name isn't known, it is thought that the name is from Americans. FWIW, it is a bend. While all bends are knots, not all knots are bends. So the EDK name really leaves a lot to wish for.
There are alternatives to the Prussik such as the Klemheist which don't jam as badly.
I wouldn't use a ring bend - the double fisherman's is superior for tying rope or cord ends together to create a sling. And I definitely wouldn't use either a ring bend or a double fisherman's to link ropes for abseil. An overhand tied in both ropes (with a 50cm tail) -aka the EDK or European Death Knot is way superior, as the body of the knot sits to one side of the line of the tightened rope, so it tends not to catch in cracks.
Finally, extending slings by linking them over and under into a reef knot is stronger than a girth hitch.