I don’t think it’s secretive. Just not well documented.
You have to write them up with the SPI bus connected and there is a diagnostic pin that you connect to the endstop pin. You also need a chip select pin assigned for each driver, which makes it hard to keep the LCD.
It would work for x, x2 and y, but it would be hard for z.
The part that is a mystery to me, but is almost certainly open source, is the ability to detect missed steps during a print and recover. That would have to look different on a CNC machine. But it would be freaking awesome.
At any rate. The low rider works great without any endstops. I would recommend working without endstops first, until you get the hang of it. When you get endstops, the dumb switches are a lot easier to use than the tmc drivers. The tmcs are supposed to skip less often at the same current, have smoother motion, and the limits are software configurable. But they are not as easy as the drv8825s.