I saw three of them on the STP a couple of years ago. Looked like they were promoting them, but they made it look like a LOT of fun. They seemed to float past me on the longview bridge and quickly climbed out of view. The next year, there was a guy riding one on the Cascade Training Series rides in the yellow group (12-14 mph average) but I didn't see him after the first three rides--after the rides started getting really hilly. I think those three people were super fit "ringers"--intended to make the elliptigo look effortless and fun.
Rodriguez Adventure
Bacchetta Bellandare
HPV Gekko fx
Custom Rodriguez Tandem
2009 Specialized Tricross
2012 Trek Mamba