I too have been wondering these things… more points for anyone who can compare the two models (and perhaps to other known standards and power measurement accuracy) 
Subscribing to see what people say…
I just got mine (Vortex Smart) thanks to the DCR post, can’t report on FE-C just yet as my ANT+ stick didn’t like Zwift (new one incoming) and my Stages is en-route back to Colorado but with the TacX app, the fact that you can run in ERG mode is pretty awesome.
Had no issues updating the firmware, pairing did take a few tries though.
Will have more to report in a month or so.
It was super cheap too at 350$ Canadian.
Does the resistance seem to work well? How quickly does the resistance ramp up? Is it smooth?
I am coming from a Tacx Swing (think old) and just used the vortex for a short while yesterday, but the resistance comes on fast, and it feels better than my old trainer. It’s impressive how it adjusts the resistance to match cycling speed.