A careful reading of the drive manuals indicates sensorless drive control should not be used at very slow speeds. This may not be a problem for rollers which normally run at high speed and where unexpected operation does not create a hazard. I ran into trouble with roll lifting tables and special rollers with high load requirements.
The first problem is that drive auto-tune may not work. The drive may be left with some default parameters based on nameplate data. These drives may be subject to unexplained overcurrent trips.
The most severe problem I experienced was with a roll lifting table. The device used a screw drive to lift the table to the roll, shaft was removed and the table lowered the roll to the packaging conveyor. On occasion, the drive failed to start in the down direction when required. The drive indicated torque limit down, but the drive did not move. The next command to start would work perfectly. At first glance, this looked like a brake failing to release, but it turned out to be the drive.
Comments – other identical lifting carts with different sensorless drives worked flawlessly. Other drives were able to complete auto-tuning.
I suggest caution in applying sensorless drives. In particular, consider high load applications or low speed applications carefully. I would have an encoder available while developing the machinery, to ensure that sensorless operation is correct. Unexpected trips, unexpected motion or failure to start have high economic costs.