You forgot to include the part about Fazua being Chinese and of inferior quality.
Maybe part of your problem is you just lack imagination and vision. You and
@Alaskan are both assuming the typical rider wants the assist at the top end (ie to 28 mph). What if they want it at the low end and want to ride unassisted and unhindered at the top end? Meaning perhaps they are riding in hilly terrain and they need the assist for the climb. Or perhaps they want the assist to provide some additional torque from a stop. But for flats, maybe the strong rider doesn't need the assist but also doesn't want any drag such that he/she can ride unpowered over 20mph.
As for riding without the battery or quickly converting an electric bike to a regular bike: today I put in 20 miles on my non-electric, came home, dropped off that bike and put in another 10 running errands on the cargo electric. Maybe for the younger and more fit rider and/or for someone who doesn't have space for multiple bikes, a system like the Fazua makes sense. One bike for multiple purposes vs several bikes for multiple purposes. I can definitely see use-cases for it and I'd personally be interested in a commuter with just minimal electric assist - one that just takes the edge off of a 35 mile commute - one that is mostly a bicycle and one that mostly relies on my power. Fortunately I don't have a 300 lb carcass to haul around at 28 mph and at 54, I still feel that I'm fit enough to provide most of the energy to power the bike.
Now
@Alaskan posts that the battery can't be charged without being removed and removal requires tools. I apparently missed that in the various videos that have been posted. That would definitely be a major drawback and would lessen my interest in the system (removal requiring tools).