As a paid Synergy user, there are tradeoffs (as you probably know). I'm willing to accept these for a side-by-side Mac workflow (or Mac + something else), where each host has a dedicated display.

For a workflow where you are also display switching (kvm etc), Synergy doesn't work well. You can technically use it when hosts are coming on/off display, but it's not designed for it. If you use a kvm-like workflow and have a Magic Touchpad, there's no easy solution without re-pairing, and I hope OPs tool works for this.