Nice to have something that is easy to use in a repair vise - gets the bench surface out of the way as an obstruction, and the orientation of the fixture can be changes at will for best access without removing the work.

Just a note: I'd call this a neck shaping or carving fixture; a jig guides or aligns a tool, while a fixture holds the work. Don't think anyone would much quibble if you called it whatever you want, but clarity suggests jig and fixture be applied where appropriate.

The other advantage to the repair vise is that it allows the neck to be clamped and worked similar to the shave horse, although it's not as much fun.