I've tried many different KVM products over the years.
The only absolutely reliable
ones I've ever found are made by a company called Raritan
They're pretty much the industry standard. Raritans can be found in many major data centers and corporate server rooms.
Not cheap by any stretch. A simple 4-port SwitchMan
model runs about $100 - 150 depending on which one you need. (Some of their other models sport price tags that can easily cause dizziness and nosebleed. )
But if you want "no BS" absolutely bulletproof hardware-based
KVM switching, this is the only
brand AFAIC. If you're setting KVM up for a client, get a SwitchMan.
If you don't insist on a hardware-based solution, then I'd definitely go with Shades'
recommendation for Synergy
. I use Synergy at home to handle my rag-tag and ever changing 'harem' of PCs and NIX boxes. Synergy is cross-platform, easy to set up, reliable in use - and free!
So what's not to like?