Zwave Generations
Zwave plus is the newest generation of zwave, the fifth generation. (It’s also called fifth GEN or series 500). The older generations are now called Z wave classic.
Z wave plus has quite a few advantages over z wave classic, although they are compatible with each other and you can have some of each on your network. The biggest difference is that you as a customer would notice right away is that zwave plus has a significantly longer range, better battery life, and is somewhat easier to pair in place. There are some additional technical improvements.
The original Leviton DZ switches were using Z wave classic, but The newest versions have z wave plus chips. It’s likely that the Vizia line will also switch to zwave plus eventually.
Leviton’s Old DZC Line
It’s not that the DZ line can’t work with a Leviton controller – – it can work with any certified Z wave controller, classic or Z wave plus. The difference is that there are some additional features in the Vizia line which will not be available with a DZ switch.
When used with a smartthings controller, the original DZ switch is updating its status, but it is using a different method update its status. ( technically it is using association instead of hail.) And that different method is not being triggered when the auxiliary switch is pressed. It’s just the way it works. It sounds like the same issue may have carried over to the new models.
The Vizia line uses hail to update its status, and I think that also gets triggered when the auxiliary tells the master to turn on, but someone else who has the device can confirm that.
It looks like the newest version of the DZ line, the zwave +ones, has been updated so that it also has hail, I’m just not sure if it is using it when an auxiliary triggers the switch.
Shopping
As far as where to buy the Vizia devices, most of the specialty Z wave retailers have them, and Home Depot carries the line on their website, but not in store. I just checked several of these and everybody had them in stock. (HAWorld Online, Home controls inc, Smart Home, Westside, zwaveproducts.com, Home Depot all had VIZIA switches in stock this morning.)
They’re really intended for professional installers, so if you’re just shopping at brick and mortar stores you won’t see them. But if you check the online specialty retailers they should be pretty easy to find. 
They will likely go out of stock if a new model as expected, but that’s understandable.
If it was me, though, at this point I would only be looking at zwave plus devices, so I wouldn’t be shopping for Vizia right now.