The ear sensitivity is not linear, so, that is the reason the volume pot should be logarithmic.
Now for the tuning, the way the software is written, you have 50 Khz of tuning range on 300 degrees of rotation and 1024 steps in the analog to digital converter (10 bit A/D). A change in position of the tuning pot with 0.3 deg. will change the frequency. Using a multi turn pot will increase the amount of movement required to have a change in frequency.
Another way of improving tuning feel will be by reducing the tuning range to 25 KHz or even 10 KHz by modifying the software, or installing a rotary encoder (also with modified software).
There is another sketch (firmware) that is using the pot in a different way. As long as the pot is in the middle position nothing happens. When you turn the pot frequency starts changing. The speed of change is increased with the angle of rotation. Once where you want to be return the pot to the middle position and you are tuned.