From what I recall it came about as a result of trying to get round the limit on number of cylinders. What they did in effect was make 2 cylinders into 1 by "taking away" the bit in between. The combustion system, valving, stroke and thus RPM capability operated effectively as though it was 2 small cylinders.
There's no real technical advantage in having oval cylinders if you can have 2 round ones instead, and the mechanical challenges of machining the bores and making rings work properly (gas sealing and oil control, not to mention what happens when the ring gets hot and expands) really make it a nightmare.
An interesting technical oddity, but of little real value.
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