I went in to ask about them early on and the people knew nothing. I was confused by ads about them that talked about 'range' I thought maybe the car couldn't run only on the gas generator and it just extended it or something.
The dealers were anti-selling them and directly hostile.
In the end it turned out just to be stupid advertising - I'm not sure why you'd talk about a 'range' when you can fill up and immediately keep going, it's misleading.
These companies have no hope against Tesla - the superchargers are excellent.