by the way, do you just stand on yours or do you do exercises?
Both. Also some seated in a chair next to the plate. Some vibration modes on the machine I have are more intense. Those I do seated. Also depends on what joint(s) you want to reach.
Two main rules...if it hurts AT ALL, back off on intensity or time and RAMP UP VERY SLOWLY.
I recommend getting one of the Chambers books I linked to above. I have not found her advice to be in error on any point.
And, of course, talk to your doctor first to see if you have any contraindications that would you preclude using the machine.