The WooLee Winder is particularly nice for even plying, as you don't need to stop to move the yarn guide as you do on manual flyers.  The tradeoff is a very slightly heavier, less responsive feel due to the inertia and friction of the level-wind mechanism.  It is very important that you keep the mechanism clean and properly lubricated for best results.  Not a big deal, just beware that it's important.  

The flyer speed ranges from zero to about 1400 RPM; a bit slower than the other flyers due to friction and wind resistance.   

What's included:

• WooLee Winder level-wind flyer
• Bobbin
• Drive band for standard flyer
• Brake band assembly for standard flyer

 Product Details:

Weight: About 1 pound (454 grams)
Dimensions:  Bobbin is 4.25" (108mm) diameter x 5.780" (147mm) overall length, 4.625" (117mm) inside length, 0.625"(15.875mm) core diameter
Capacity:  64.2 cubic inches (1052 cubic centimeters)

Tachometer Sensor Magnets:

The tachometer sensor magnets are required to display the RPM of the flyer if you have the LCD Display.