Great idea for the technicians. That's gonna require the same prep work as a solder joint, only you can't twist them together.
How do you flux the wire without accidentally lubricating the sticky stuff?

I twist and solder ,tape and then cover all with liquid rubber ,you can find it in Lowes /home depot  ,comes in a container like PVC cement ,with a brush  in the lid . also great for sealing the back of stock connectors .

I have used those connectors, and they work fine on wire that is clean and not corroded.  They must have a solder that somehow self "fluxes", as they solder the wire well.  It takes a little practice to learn how to get the entire connector hot enough to solder and shrink properly - without overheating anything.  I keep several sizes in my electrical repair box.

I think the connectors are a bit bulky for use to build or modify a wiring harness - they make the wiring bundle thick and stiff as they don't flex.  I prefer to just splice the wires by stripping off a small length, twisting them together, fluxing and soldering them, then use a small piece of heat shrink tubing.  When splicing several wires in the same area I stagger the splices a bit to avoid a bulky bulge in the harness when I use black tape to create the outer covering.

Using the bullet connectors to repair or modify the harness is really a great way to make a factory looking project.
http://vintageconnections.com/