I went for the bolts on the back as my focus isn't that low but was getting uneven wear as the car does get driven fairly hard.

To be honest the wear on the front was worse but thought I might as well get the rear bolts fitted at the same time. The settings are meant to assist grip on track and reduce the uneven wear but I haven't been on track since they were set up so can't confirm that but seems to drive ok on the road

al