I started seeing ads for these a while ago and got one a couple of years ago for bushcrafting adventure and general utility. Having manual tools on hand is good, both for emergency power-down use but also off-grid crafting. Hand saws, hammers and hand-drills are all reliable, if sometimes arduous tools to make use of.
A scotch eyed auger bit is a type of tool you can use to create holes either dry or wet woodworking applications. The “scotch eye” is the hole at the end of the auger and its purpose is to enable easy handling and additional leverage.
This particular one has a 20mm auger bit (8/10th") with a single flute that runs for 9cm (3.5") for a total shaft length of 15 cm (6") and terminating at a round pipe eye of 18mm (7/10th"). It appears to have been made from a 20mm hex ended drill bit welded onto the eye segment.
The cutting tip of the tool starts of with a self-tapping screw-head that ensures good purchase and correct placement of the auger for optimum boring. The cutting face of the auger is set back from the leading edge of the flute, which has the effect of being a scoring/ cutting edge, around the circumference of the bore being cut, this ensures a clean cut and smooth finish.
The eye is set perpendicular to the auger shaft, such that a branch can be fitted through it in order to make a handle to easily turn the auger and bore into even hard, seasoned timber. Once the tip has bitten, and the cutting face engages, the long flutes will guide the auger on a straight path through the wood, so be sure to get the initial line straight.
The eye is also a means for producing peg ends that will fit into the hole bored by the auger. These can be whittled manually and test-fitted in the eye or hammered through the eye to shave/ scrape the pegs down to size. The remaining hex of the original drill haft is lined up to nicely be hammered upon, which was also a nice touch.
The eye is sightly narrower than the auger bit, which means that pegs cut with it will be -slightly- loose, which can be a good thing depending on the situation, but a long as you take it into account you would be fine. If I were making a pole and branch ladder, i'd be lashing the rungs in, regardless. The length of the tool allows for quite deep (6") cuts to be made. This is plenty deep enough to make a rocket fire from a log like a Swedish Fire torch. Deep enough that you could probably pin log cabin logs together, though that would be a lot of hand cranking. pegs used in this fashion are called treenails or trennals and have been documented back as far as 7000 years.
I've seen some Scotch eyed augers with one face of the eye being sharpened to bite into the peg-wood, whilst the rear face is hammered and mine lacks this. I'm not certain it would be necessary and have done just fine without, but if you were intending to make a lot of pegs out of cut lumber it might be advantageous. I whittled down this segment of green branch the power company lopped from one of our cub-side trees, and its made a very good handle in less than a minute. I did this when my previous branch/peg handle snapped whilst mid way through boring a hole through a particularly seasoned piece of recycled timber. A minor setback, quickly addressed with a field expedient replacement and I got the job done. 
One thing that hadn't occurred to me until I was well into my boring task was that the swerf material (wood chips) I was boring out would make excellent kindling, even in wet conditions ,the inside of most wood stays dry. This would be even more true with more resinous woods. I've used the auger on branches and logs I've found trail-side as well as dressed timber both fresh and reclaimed. 
One word of advice, ensure your leverage stick is a good fit and smooth or you'll hurt your hand whilst boring. Wear gloves. Be sure your angle is correct when starting off and check for drift. All in all its a very simple and elegant tool and at only 175g (6.3 oz) its an easy add to your bushcrafting carry. I made a simple leather pouch for it with belt loops, so I can take it with me along with my belt knife and trail hatchet. I imagine myself making tripod stools and even legged benches with this tool, as well as through-holes for future furniture projects.
