Unfortunate timing on my part. I just bought ExtFS on Sept 28, 2015 and El Capitan came out on Sept 30. Just for kicks, I had a USB install of OSX Yosemite and I upgraded it to El Capitan and then ran the latest dmg version of Paragon for the ExtFS package and the installer ran fine, but on boot, although it showed in the System preference pane, it did not work and gave an error when I tried to launch it. An EXT4 drive was not recognized either. No biggie because that was just an extra USB version. I know that they did some work in El Capitan that may prevent third party drivers. Is someone working on this product to work with El Capitan, as it promises to be faster than Yosemite is on two of my machine.