I'll have to take some pics later to further demonstrate what I'm saying, but for now, here's a few links to pics off the web to help...
Those crimpers "with the extra bit" that you're referring to are like the commonly-available cast steel crimpers from Klein, like these:
http://ecx.images-amazon.com/images/I/41w-QeuQ8rL._SY300_.jpg
Note the little tooth in the jaw. These are actually designed for crimping UNinsulated terminals. Let's face it, though- they work well for insulated terminals, and we've all used it for an installation with strictly insulated terminals throughout. It's "wrong" as it's not what it's designed for, and it makes a crimp that's not to spec in terms of swedging the open side of the terminal and it overly-deforms the copper wire. But again we say "this ain't a moon shot", and it works quite well even given that it's "wrong".
Now, the actual, correct tool for insulated connectors is more along the lines of these:
http://www.stridetool.com/tools/electrical_datatools/crimper_ie145187.gif
Specifically, the "hand side" of the hinge on IE-145, and the entirety of the dies on IE-187 (though I can't discern if they're actually for data connector terminals- tool looks REAL similar to the crimper for DAMA30 and UYK20 pins, which were a severe pain in the ass, but that's another discussion). If you look at slot "A" on IE-187, you'll see a bowed surface on the left, and a cupped surface on the right. The bowed surface is where the "open side" (honestly, a better choice of words would be "seamed side"- but no matter the terminal, a seamed connection always has an open side where the material is not joined to itself, because they start out as flat sheets of material that are then formed into connectors, whereas unseamed connectors start out as tubing). So, getting back on mission here- the open/seamed side goes against the bow (or the left side of slot A on IE-187), and the solid/unseamed side goes against the adjoining, cupped side...
Finished product should look something like this:
http://m5.i.pbase.com/g3/84/622984/2/94465955.Sq9IoVXH.jpg. Granted, those are both FAILED connections, but it's early, I'm still trying to wake up, and I don't wanna track down my good camera. Those are failures for two reasons. The one on the left is unevenly crimped, the one on the right appears to have been used with a wire that was too small, as it's not full of material. The one on the left would probably work just fine for mobile electronics. The one on the right would likely not pass the "tug test".
Note that the "open side" is at the top, and has clearly been pressed into the bowed side of the die. This first tightens the material, then shrinks it as it pushes it around and down into the material inside the body. When it does this, it also swedges the material inside, deforming it and making sure everything is compacted together, achieving lower resistance in the connection and a mechanical bond.
I will add that crimping, then crimping with a smaller die, is dounterindicated. You will break strands doing this, and stress the hell out of the wire. Not good for a high-vibration environment. But it works for him, so that's fine. I suspect, if I know our Aussie friend, Oldspark, like I think I do, that he ends the job by harnessing all the wires into a bundle and then taping together- creating an excellent strain relief. I do it myself, just make sure not to use the cheap tape- it leaves a mess if you have to go back and change things. ;)
If it seems I know way too much about this stuff, it's because I do. I had to set through a week long course on doing this stuff when I started working on Uncle Sam's neat toys.
More than you'll want to know about crimping:
http://www.globalspec.com/learnmore/tools_instruments/crimp_tools
Though right off the bat I note one glaring inaccuracy in their document. They say that "bullets are crimped into their shells". Well, maybe. The vast majority of bullets are NOT crimped. Some are, especially those used in tube-magazine rifles and shotguns. Another discussion entirely, outside of the scope of this document. (Can you tell I also handload ammo?)
"Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"