USB passthrough mousepads won't slow your click.

No, not in any way you’d ever notice with a wired mouse.

USB is a digital protocol with error correction built in. A good-quality passthrough hub on a mousepad is just a short extension with a built-in splitter. The latency is measured in microseconds — orders of magnitude below what a human can perceive. Your mouse already has a polling rate that’s way slower than USB 2.0’s bandwidth, so a few extra inches of cable don’t matter.

The only caveat: terribly made hubs. Cheap, unshielded ones can cause voltage drop or signal degradation if the cable is thin or long enough. But the pass-through hubs on decent mousepads (think Razer Goliathus Chroma, Corsair MM200, etc.) are fine. If you’re buying a $10 gas-station mousepad with a hub, maybe skip it.

Stick with a reputable brand and you’ll never think about it again.