better late then never, here is my input on FlyXii
I the happy owner of 2 FlyXii frames, for many years now. One is my current road/gravel bike (refurbished from my crashed MTB). The other is my wife's bike.
The first is rock solid (multiple races), the second is strong enough for my wife but I would never hammer any trail with this one.
They are honest, you can trust you will get your bike but the quality is unknown till you receive the frame. Also I believe they know nothing about bike and I would not expect any sort of support from them.
Why would you buy from them? Well, because they are so cheap! Up to you to take the risk or not