We have ground that is both rocky and has draws and hills. We tried the 4 Link Closer on one row last year and found that it prevented some of the issues we were dealing with.
The main improvements were better row unit performance around the draws and hills due to increased tail section travel. The increased travel also allowed smaller stones to pass under the row unit and not get caught in the closing wheels, as sometimes happens with spiked closing wheels in our situation.
We decided it was good enough of an improvement to use them on the whole planter this year.