I remember meeting Dr. Robert Wohleb many years ago at Pittcon after he left J&W and he was just beginning work on the spinbar extractions. He was actually doing solvent desorption with them. It did reduce the solvent needed quite a bit, and was concentrating the samples because they were putting the spinbar into a 1L sample then extracting it with 1-2ml of solvent. They would just put in in an autosampler vial with solvent and after some time remove the bar, cap, and shoot. Really simple.
There was another thing they were working on that used the coating on the liner of a bottle cap instead of the stir bar. You cap the bottle, rotate it over night or however long was needed, then put the cap on a smaller vial with some solvent and shake it to extract the target analytes. I don't think I ever saw that one go into commercial use though.