King pin IS what it is called.....
Point being made was that the 'stabilizer' in your link is for a 5th wheel with a gooseneck adapter vs standard 5th wheel king pin
Your link shows one with a BALL that a gooseneck adapter would sit down on
Standard has a 'cup' that king pin would sit inside of
As for need......personal choice
When we went Full Time I thought it would be good idea.
First off it took up storage space
Secondly it took too much time/effort to set up/get adjusted
Thirdly...it did NOT make any difference
I found a much easier way of stabilizing or 5th wheel (works on travel trailers too)
After leveling side to side I set wheel chocks and a set of X-Chocks
That helps prevent fore/aft motions
Disconnect for tow vehicle and level front to rear using front landing gear legs (or tongue jack)
THEN lower front 1" below level
Set rear stabilizers/jacks....SNUG
THEN raise front back to level
Solid set up..... other then a little suspension/tire bounce which can only be eliminated by placing jacks fore/aft of tires.
Kin Pin Stabilizer........IMHO NOPE