Like Robby said... buy the best servos you can for less than $8. Centering/accuracy is not important either. It is a closed loop system and will sync the engines even if the servos are inaccurate. During development I just used double sided tape to mount servos to the test stand. Some times a servo would come loose from being fuel soaked. It would sync the engines with the servo being loose, vibrating and moving arround.

If you use a really fast servo and get oscillations you just have to slow down how fast the TwinSync moves the servo by changing the timing in the programming mode with the rotary switch in position 4.

The most important thing like Robby said is to extend the endpoints as far a possible. What you want is 100 rpm change for 1% servo movement rather than 500 rpm for 1% servo change.

Bill