This new adjuster is a direct replacement of your existing piece. After decades of exposure to an engine compartment these adjusters become brittle and eventually break. Even if you find a "good used" cable the adjuster piece is still aging out. As far as labor goes if the only problem is the adjuster then just replace the adjuster. No need to R&R the entire cable which requires more labor plus you add the risk of creating a leak down at the transmission end.
The original design by Mercedes has actually done very well given the materials available to them. This was also back when their motto was "longevity." Note that any threaded screw/nut combination requires the parts to be made of the same material if they're going to last. A metal adjuster would quickly wear out the plastic nut. An all metal setup would wear out the stranded cable constantly moving back and forth through the adjuster. Mercedes' final design focused on the stranded cable outlasting the rest of it. This new adjuster piece maintains their design with more mass and modern polymers.
As mentioned installation averages 15 minutes including removal of your old piece. This adjuster installs in place without cutting or separating your cable in any way. The alternative is replacing the whole cable which requires either a mechanic or a longer DIY project under the car. Replacing the adjuster is 20x easier. If Mercedes offered a cable and also offered just the replacement adjuster I'd get the replacement adjuster and leave the rest of the cable alone. The adjuster lets you skip the mechanic/labor costs/down time of replacing the whole cable.
Symptoms of a bad adjuster can include the transmission appearing to slip or flare as well as late shifting or early shifting. All of these conditions will eventually cost you a transmission.
This demanding little piece has taken over a year of R&D including months spent testing over 100 design variants. After long drawn out expenses + site seller fees + PayPal transaction fees + shipping fees it's barely worth it on here because of all the middle men. If it helps I can go a bit lower without the warranty. To protect intellectual property for now the item you receive will look different from the images shown.
I did all of this to help keep these cars on the road. It would be so much easier if Mercedes would just stop discontinuing parts for our older cars but that won't change when they make more selling $2,400+ headlight assemblies for their newer cars.