I have used Synergy, Mouse Without Border, Multiplicity, and more. They all suck. They. ALL. Suck.
Every single one of them needs to be reconnected multiple times a day. I fix this by using a schedule task that restarts them. lol
They ALL have clipboard issues where the clipboard stops working at some random point in the day.
Some of them have system breaking issues like the Synergy login screen issue. Where if you are at the lock screen (as happens throughout the day) and you move your mouse to another screen, your mouse is 100% stuck on the other screen. The only way to recover your client computer is via the power button. So take all that work you left when you got up to go to the bathroom, take it all and flush it down the toilet. Thanks Synergy. Fuck you Synergy.
They all have issues with more than two machines. Sometimes you can only access the left 100 pixels of a certain machine. Who knows!? It's fun isn't it!? Sometimes a specific screen will just... stop working. Who knows!? You were just sitting there. And now your workday has stopped.
Fuck you Synergy. Fuck you Mouse Without Borders. Fuck you Multiplicity. You all suck. You are all half-ass attempts at something that very much needs to "just work".