Thank you for your responses. All appreciated.
Dave, possibly no advantage whatsoever. Just as I said fascinating, and, as a model could be interesting.
Jeff, thank you for the link. It contained useful info and well worth the read.
John S, I agree, but still fascinating.
Perhaps it's my curiously twisted brain but quirky = interesting and, let's face it if I ever build it into an engine model it is just for that reason, interest. As for wear, models typically run for minutes at a time and therefore unlikely to wear out in my remaining years.
I assume many of these linkages were invented to circumvent patents on existing crosshead or parallel linkage designs. Or, perhaps were the precursor.
Anyway, following Jeff's web link. Since Robertson lived (1789 - 1864). His design seems to be somewhere between his birth and 1852 when his firm collapsed.
My Guess, from the dates in Wikepedia somewhere between Watts' Linkage 1784, and Chebyshev's 1878
All interesting but not essential to messing about in the shed.