Anyone have experience with inexpensive Flashchip FCM32F103 microcontrollers?

[globoy]

I'm looking to see what development environments can be used (e.g. can they be used in Keil uVision or STM32CubeIDE) and if their USB port can be used for programming and/or as a USB CDC class serial port by code running on the chip (CDC serial is most important).

They are nicely inexpensive at LCSC.  For example 0.80USD for 1:

https://www.lcsc.com/product-detail/Microcontroller-Units-MCUs-MPUs-SOCs_Flashchip-Microelectronics-FCM32F103C8T6_C3151837.html

So far I haven't found an english spec for the part but they're definitely STM32 knock-offs with some kinda neat features such as 5V operation (power by USB w/o regulator?) and a Cortex M4 core.