I would recommend you read the instructions on them
And then spend some time playing with them to get the best response for your robot control.

The speed adjustment for what you want you just put it at full speed and leave it there. this function is for things like trains or boats you may not want to go too fast!

Frequency control Low frequency gives better low speed grunt or pushing power, high speed better power at high speed in the middle a bit of both

I use this speedo for an axe motor control so I have got it set on low frequency it seems to get things going a bit quicker the motor probably doesn't get up to full speed anyway