Are unicycles more, or less, efficient than walking? (or are they just for fun, entertainment and exercise?) There are various sizes and shapes of (pedalled as opposed to electric) unicycles.
It is possible to buy them with large wheels, supposedly for road use.

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Question
I imagine that the lack of a freewheel mechanism, having to brake by back pressure and the effort of balancing mean that they are inefficient and require constant effort. Also there are no gears for going up or down hills.
Does travelling by unicycle have any advantages over walking as a mode of transport? Would level city roads be most suitable? Does it ever become easy and/or completely subconscious with practice?
With a competent rider, a unicycle is far more efficient than walking. As evidence of that consider for example:

World 24 hour distance record on a unicycle : 453.6 km
One hour unicycle record : ~30 km
Record unicycle time on Karapoti Classic race : 4:11:43 (50 km off-road MTB ride with ~1500 m of climb)

These feats are all well beyond anything anyone could complete on foot.

For comparison

24 hour walk (on a track) 216.621km by Claudio Sterpin (Italy) on 19 Oct 1986 in Milan
24 hours walk (on the road)  228.930km by Jesse Casteneda (USA) 19 Sep 1976 in Albuquerque
1 hour walk 15,577 metres by Bernardo Segura (Mexico) 7 May 1994 in Fana



24 hour ride (indoor track) 941.872 km by Christoph Strasser (Austria) 14–15 October 2017 in Switzerland
24 hour ride (road) 915.39 km by Ralph Diseviscourt (Luxembourg) 11 July 2020 in Luxembourg
1 hour ride (track) 55.089 km by Victor Campenaerts (Belgium) 16 April 2019 in Mexico
Record time in Karopoti MTB  2:07:57 by Anton Cooper from Woodend, New Zealand in 2014.

 from https://en.wikipedia.org/wiki/List_of_cycling_records#24_Hours_record and http://www.karapoti.co.nz/files/3915/8322/1936/20_Fastest_Karapotis_03.03.20.pdf no times found for walking the route.
It appears that in terms of distance-covered-in-time, or time-to-cover-distance, unicycling is very approximately twice as efficient as walking and half as efficient as bicycling.