I got one for my daughter. The erratic ticking eventually became a distraction when she was studying, so we have retired it for now. But we got a lot of amusement out of it.
That's pretty genius for many ADHD-type folks. Only problem is a modern household has many clocks in view, so you'd need to commit to just not setting them.
Easy enough for wifi enabled ones: a UDP broadcast to discover other clocks on the network, then sync how you will.
For non-wifi-enabled clocks, perhaps something like a CH572 would do the trick: a $0.20 RISC-V microcontroller with BLE support that all the clocks in the same vicinity could use to talk to each other.
You could really mess with your neighbors if they had the same clocks and you were within range...
Yeah, the main problem with this project is you have to find a silent 3.88 analog clock to attach it to.
Last cheap clock i've tried was silent on half the circle and kinda buzzy on the other half. It had seconds so that meant the ambient noise changed every 30 seconds...
Oh wait. Maybe I should open it up and remove the seconds needle. Time for a totally analog project!