here it is from Deere.com:
Automotive cruise/SpeedMatch and MotionMatch control upgrade kit consists of cruise and accel/decel/resume functions, SpeedMatch, and MotionMatch switches. This kit fits all 3120-4720 eHydro models cab and open station.
Automotive cruise allows the operator to accel, decel, and resume set speeds. SpeedMatch allows the operator to preset their maximum eHydro speed for operation. Ideal for applications requiring set speeds (spraying/aeration).
The MotionMatch switch allows the operator to make instant adjustments from short to long rollout and is ideal for operators that frequently change jobs (for example, from mowing to loader work)
SpeedMatch also works like a creeper gear.
This is a $90 uppgrade that is a very easy install. It is well worth having, but also makes a nice add on for later. (Print out the description with part numbers and lay it out conspicously before christmas, fathers day, or...)