I have 50+ Leviton dimmers working fine with the smart generic dimmer since it was updated. They report physical and digital interactions virtually instantaneously.
The firmware update is totally needed unless you want to use the "non-smart" driver and get updates via polling which is all that can be done for the older z-wave (non-plus) devices.
The only source of the firmware upgrade I can find is HomeSeer (unless you are a Leviton installer). Painful but necessary if you have invested in what are otherwise great dimmers. See the link for more info.
Hope it sorts the issues out.
