John Stevenson advocated the benefits of the original vice, but I think John might also accept it's limitations. The very shallow depth of engagement on the shallow jaws is useful for small jobs. But for bigger jobs a bigger proper machine vice is needed.
The Dore Westbury has a long X axis, but this is negated by the original vice for lots of common operations.
So you want to do forked ends on an eccentric rod (sorry John for mentioning miniature steam locos). You clamp the rod in the original vice, and there is then insufficient Z movement to do the milling.
Most cylinder blocks for miniature locos require great ingenuity to mill the port faces and ports using the original vice.
In most cases a proper machine vice would resolve all these problems.
I havent found the moving jaw to be particularly 'precision' in operation – but perhaps mine is worn after 35 plus years. I have to add a bit of shim under the moving tongue underneath the static jaw.
On the bed is a nice slot, and it would have been a nice feature of the vice to have a tongue to engage in same for parallel work without having to DTI up the vice if removed for using angle plates etc.
My old late friend Albert North had a Dore Westbury which he used extensively for milling on miniature loco parts including 2 5"g Brits, a 5"g 9F, a 5"g Pansy, and a 5"g Firefly, and much else besides. He had a proper machine vice on his. The raised height required on the column caused no problems.
Cheers,
Julian