Really enjoy the DTM...and thus, my first response ever.
Below is the citation in the 2016 regs which I understand carried over to this year as it relates to Brake Bias. While it is paddle shaped, it is made to spin both anti/clockwise quickly. I thought this was a common design across all 3 manufactures but not entirely sure. If it is, the design isn't regulated that I can find in the technical regulations but when watching the drivers use it it seems like a pretty quick and easy way to adjust brake bias.
From videos it seems like the spinning mechanism has detents to prevent it from freely spinning.
"The brake force distribution between the front and the rear axle must only be modified by use of the brake balance adjuster. The distribution of the brake force may be adjusted by the driver whilst the vehicle is in motion. Only a purely mechanical construction (see Z70) may however be used for this purpose. Components under current and pressure accumulators are explicitly prohibited for this construction. Beyond this system, there must be no other device inside the car which allows for the adjustment of the brake force distribution whilst the car is in motion."