I like the SR spoiler better, myself, for style & efficiency.
That UK spoiler would increase drag slightly (upward angle). I'd bet the SR spoiler actually decreases drag slightly (vs. none at all).
As for aftermarket, there are almost certainly other options already available in various countries, but you'd get killed by shipping.
Got your wheels yet?
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View my fuel log 2015 Micra S manual: 5.0 L/100 km ... 56.5 mpg (Imp) ... 20.0 km/L ... 47.0 mpg (US) ...