We had a few milling machines that used this system for speed control of the cutting head. It was controlled manually, with a hand wheel on the outside of the head. Worked very successfully and was very reliable in that situation.
Yes, I've seen those before on millers.
I had a bit of a soft spot for the CVT on the Volvo 340, if the belts were replaced regularly and the vacuum pipes were kept in good order, it was reliable and worked quite well. The speed was locked down to the lowest ratio in reverse on the Volvo, I seem to recall that the early DAF CVT also worked in reverse, and you could go at full pelt backwards!
Anyone that's worked in the food industry will also remember the Krones Canmatic labellers which used the same system, but an air operated pulley and everything 3+ times the size of the Volvo.