Similar to fasteners used on aircraft. The key design looks much better than the Hi-lock hex drives which have a tendency to round off – meaning you have to drill out a titanium fastener in some awkward place and position!

The Hi Lock that I used had the aluminium snap off heads on the nut, the hex socket was only needed in case the bolt rotated while the nut was tightened, not to unscrew the assembly. I believe there are more conventional nuts for certain applications.

Theft of aluminium road signs, cast iron manhole covers and bus bars from electricity substations is common these days. Probably getting less as China is cutting back on its scrap metal imports, so the price is dropping.

Depends, when using Hi-Locks in structural parts and repairs most of the times it's an interference fit, so the hex drive on the collar most often than not snapped off before the fastener could turn – given that the hole was reamed to the correct size beforehand.

Where hi-locks are used to retain brackets floor beams etc hex nuts are used not collars. Sometimes the fastener rotates with the nut and then you'll need the key.