Here are a couple in Belgian service, one in the dunes, by the look of it, sometime after the Yser. The other is no longer fit for purpose as the rueful rider examines it after it has been hit by a shell.
"Sometimes things that are not true are included in Wikipedia. While at first glance that may appear like a very great problem for Wikipedia, in reality is it not. In fact, it's a good thing." - Wikipedia.
Thanks for those, interesting photos - as for the second picture, could be a military motorised unicycle, leaving the hands free for, say, a Lewis gun?