Quick question for you guys since I know a couple of you guys are time ATAC fans, are the ATACs free float or are they spring returned float like my Shimano M520s?

I'm thinking I need a new clipless system since after increasing the release tension on my M520s (and thus, also increasing the tension against any float movement) I've been getting sore knees on longer rides. Since I'm not totally comfortable with having low tension on my Shimanos I'm looking to replace them with ATACs in the near future.