There is a thread comparing UW and Lunicycle.
The Lunicycle wheel is oval, and according to @slamdance this smooths out staggered movement from pedaling (half-rev to half-rev kinda stuff).
Either they go slow because they just learnt it (which is supposed to be much easier), because the oval wheel makes it awkward to go fast or simply because it makes the video look more relaxed and smooth (marketing purposes).