What is the difference between the Pro 845 electronic tension head and Silent Partner electric tension head?

The Pro 845 tension head is the electronic tension head, which makes stringing much faster and easier:

• It has the microcontroller chip to control and monitor the tension; it provides 1 pound tension accuracy
• Easy to calibrate the electronic tension head.
• The two-way DC motor to pull and release the string. You do not have to use muscle to operate. You just need to push the button to pull and release the string.
• The voltage deviation of the local AC power line has no affection on every tension pull.
• Fuse protection
• LED tension readout to display the tension setting
• Pound/kilogram selection switch to select the pound or kilogram operation
• Precise tension on every pull
• All-metal diamond-coated string gripper
• 2 years warranty on the electronic tension head
• The characteristics of the electronic tension head are constant pull and precise tension on every pull.

The Silent Partner tension head is the electric tension head:

• The Silent Partner uses the 1977 General Electric AC motor speed control circuitry. This circuitry is used to control the speed of the AC motor, not the torque of the motor. Therefore, the tenison is varied on every motor pull. The tension deviation is about 5 - 10 pounds on every pull. When the AC motor gets warm, it lowers tension.
• Can not calibrate the electric tension head. There is no way to calibrate the tension head.
• The AC motor only turns clockwise; can not turn counterclockwise. Therefore, The string gripper can only be able to pull the string, it can not release the string. You have to use the hand to re-wind the string gripper counterclockwise to release the string. you need to use muscle to re-wind the string gripper.
• The voltage deviation of the local AC power line affects the AC motor turns. Therefore, the AC voltage deviation affects every tension pull.
• No fuse protection
• No LED tension readout
• Only has pound selection switch
• Varied tension on every pull
• Plastic string gripper
• 1 year warranty on the electric tension head
• The disadvantage of not having two-way DC motor and LED tension readout is: varied tension on every pull, not easy to release the string, no way to calibrate, and time consuming.