It’s DF because those are the initials of the creator, Daniel Fenn.
As a rough comparison, my average riding speed on my recumbent Trike (19kg) was 17.4 km/h over 44,000km. My Milan Velomobile, weight 27kg, averages 24.36 km/h over 23,000km. And I am a fat woman nearing 50 years old. I am less fit now, due to age etc, but the efficiency of the Milan massively helps. We cruise at 35 km/h and the only issue at that speed is the wind noise in your ears is rather disturbing.