I've had mixed results with the 4000. I have a Natural 4000 from 1997. Every key still works great. I also bought one in 2016. That one had sticky keys (space)

I've had mixed results with the 4000. I have a Natural 4000 from 1997. Every key still works great. I also bought one in 2016. That one had sticky keys (space) that never worked themselves out. It was by far inferior.