The complexity isn’t actually the most off putting thing.
It’s the total perfection required in the rigidity and guiding of both the tool and the workpiece.
Rose engines benefit somewhat from a mechanical reduction in the pattern to the work – especially at watch sizes.
That isn’t true for a straight line engine.
It’s a bit like how a cheap light surface grinder will make nice looking ground parts, but it takes a rigid heavy one to hit tiny tolerances and be flat to bugger all. The cut is smaller, but the rigidity and perfection to guide it is much higher.
Still one might turn up, or I might revise my build plans and make one.
still hoping for the simpler solution…
Dave