To my knowledge all 40 thru 50 series 4WD had the single stick shifter. Personally once one is used to the two sticks, for me that is preferred as exactly as Tbone eluded to, there is a lot less arm movement to change ranges and it can be done differently as it is possible to then shift the gear portion of the tranny while the range is in neutral to better facilitate shifting with less grinding or abuse, something that is impossible with the single stick. As for two levers being more complicated to actually use, guess that depends on ones eye/hand coordination.
A friend who was service manager years ago once said something about the reason Deere went to one stick over two was due to, and be honest now admit you've done it...being in hurry and distracted and shoving the range lever into park with the gear shift still engaged

That issue is impossible with only the one stick.
The key to being able to shift the range on the fly with the Quad besides experience is using the foot throttle, an extra mostly only seen in the 4WDs. It makes all the difference
