Update:
Found some time to replace the driver's side of the endlink. Thing about using an adjustable endlink is that you only have to replace one side. The passenger's endlink is still a factory piece.
So what's the big deal with using this?
Ideally, the sway bar should not be loaded at rest from factory. Of course, the loading depends on the "wet" weight of the car, ie changing fluid level, driver's + passenger's weight. The goal is to get close to zero preload on the sway bar and even if it deviates from zero, let that deviation be small.
After installing the Eibach springs on factory 15", the front end will drop about an inch and with the fixed endlinks, that means the sway bar has to be preloaded at rest. The one way to test this is try to remove the endlink when the car is at rest with 4 wheels on the same level. Sounds impossible but it is in fact easier on the smart car. If the bolt on the endlink doesn't slide off the sway bar (or the side tab of the strut tower) easily, then yes you have a preload.
Now, the sway bar doesn't just prevent roll when cornering but it also prevents roll when one of front wheels hits a bump on a straight line. Reason being as the wheel moves up, the damper compresses along with the spring. This results in the strut tower attempting to move up, pulling up on the end link and thus on the sway bar. But of course the job of the sway bar is to minimize the movement of the strut tower. Another way to look at this is if the strut tower tries to move up, the job of the sway bar is to minimize that movement, thus "anti-sway".
After the installation, I drove around my usual routes, since I know where the road surface disturbances are. No hard data to back up but all I can say is that the bumps are less sharp and shocking on the front end.
Not a must-do mod but a good to have mod.
Here's a pic of the factory piece:
Today
Linear Mode
