KVM's suck. Or rather, they used to suck. I haven't used one in a while and we use remote access software to log in to computers now. The ones I used had issues with switching different resolutions, losing focus of the PC it's on, needing rebooted, hardware incompatibility etc.
I've used dozens of different ones and they all had a weird quirk or two. You don't really know how it'll work till you hook it up to your specific computers and hardware. I had one that didn't like Microsoft Intellimouse, I had another one that only allowed 1 resolution, and I had one that needed to be reset at random intervals or it locked up.