I find that I can more easily regulate speed with a knee lever than with a foot control. I have no joint issues, and have only started using a knee lever in the last 6 months.
I have learned that not all knee levers are created equal. I have a 15-90 in a #40 cabinet with an awkward lever, and a 66-16 in a #40 with a very ergonomic lever. The 15-91 in the...treadle looking cabinet with the straight legs is also very comfortable.
The 101, tho, is in a #40 library table, and that lever looks much like a dog-leg tongue depressor, and it is mounted on the left! I have not tried this one yet.