I saw one in a museum a couple of years back, I don't think the lack of cylinder head heat losses, can overcome the disadvantage of all that extra complexity.
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2016: 128.75L for 1875.00km => 6.87L/100km (34.3MPG US)
2017: 209.14L for 4244.00km => 4.93L/100km (47.7MPG US)