My mac mini is practically unusable after updating to Sierra. I am presumably suffering from the Logitech mouse problems reported here: http://forums.macrumors.com/threads...ce-after-macos-sierra-update-updated.2000089/ The cursor pointer is laggy. It seems worse when the pointer is over an application window, and maybe worse with some applications (like Chrome) than others. I've found that hitting the Escape button on the keyboard is a "fix", but I have to do it so often I will wear out the escape button! If you have updated to Sierra, and your mouse is working perfectly, please report what brand and model of mouse you have! I am sick of this problem, am seeing no solutions, and want to just solve the problem with a new mouse. FWIW, I use a USB keyboard (old-school Unicomp) and no issue there. The computer is a late 2012 Mac Mini i7 (the last good Mac Mini, IMO!) so no Bluetooth LE, so would prefer a mouse with a receiver rather than Bluetooth (or one that does not eat batteries, which I think is difficult without Bluetooth LE). As well, I am left-handed, and since Logitech stopped making their left-handed mouse a few years ago, will need to be an ambidextrous mouse. I do have an Apple mouse somewhere, recently moved have to dig it out from a box! It will do in a pinch, but really don't like the Apple mouse.