It basically feels like a wired mouse, no lag at all, with one annoying exception. When CPU is under heavy load, the cursor may slow down and then accelerate suddenly, which is very annoying, especially on a $150 mouse. I have a 28 core XEON CPU, so this should never happpen. Not sure what will happen to slower systems. This happened often e.g. when I encoded movies with Handbreak. I had to use a special utility to control how processes run on the CPU (I limited Handbreak or other heavy programs to use half the available cores, leaving the other half free). This seems to have resolved the issue. But Logitech should not be relying on the CPU to do the heavy lifting here, hence the 4 stars.