Heck Boomer. I was just going to stick it on there. Now I have had to study a 40 page document.
. Anyway the answer to one of your questions is in parallel according to diagram 2 below. If parallel then no centering spring although the servo saver is sprung to center quite stiffly. From feeling the servo inerter I made with my fingers I suspect the inertance is quite high. A long lever will help. It really would need one fewer set of gears as I suspected previously. You can kick it with your fingers and it will rotate all the way to the stop and reflect back some though. Thus friction is fairly low. I will study that doc some more to see where your second question comes in.
Pics 1: schematic of an inerter. That looks just like my servo setup does it not. If you have never peeked inside a servo there are at least four sets of these reduction gears. Note I have cropped out the disturbing parts below the diagram. Pic 2: 2 different ways to hook up your inerter on a car suspension. The shock is box c and the inerter box d in this series. Pic 3: An actual inerter. Note the huge multiplication of the inertia compared to the weight of the device.
john