The 680EE/S was a 680EE with a Stereohedron (extended line contact) stylus. It was the non-calibrated version of the calibrated 681EE/S. The ‘calibration’ just meant the 681 cartridges were individually measured to conform to certain frequency response limits, whereas the 680 cartridges weren’t. In most respects the 680 would have been the same as the equivalent 681, but slightly cheaper because it didn’t have to be individually measured.
The 680EE/S and 681EE/S were slightly better than the standard elliptical stylus 680EE, due to the benefits of the Stereohedron stylus over an elliptical, such as lower distortion, and lower record and stylus wear. The Stanton 680/681EE cartridges were the second highest level of the 680/681-series, just below the top level 680/681EEE models, and can be considered to be somewhere around Shure M75ED, M91ED or M95ED performance level, as those were the second highest Shure cartridges below the V15 Type II and Type III in the 1970’s.
The Pickering XV-15 was Pickering's equivalent to the Stanton 681/681-series - the only difference was the name on the side, and the stylus and brush assembly. The styli interchange between the Pickering XV-15 and Stanton 680/681, and there are roughly equivalent models between each brand. In the case of the Stanton 680EE/S, its closest Pickering equivalent was the Pickering XV-15/757 S, which was very similar, and had a Stereohedron stylus.
It’s a moving iron cartridge, quite unlike the MM Stanton 500, and quite a bit better.