I think Z-wave has been or is in the process of being superseded by just using Wi-Fi. I do not recommend investing in Z-wave gear.
Z-wave has a much smaller threat surface area and requires no internet. In fact, it requires no central controller at all, as you can have controllers in every room for scene automation. The internet connected hubs bring a lot of shiny features to the table, but they're completely unnecessary for local automation. Even better, communication forwarding is part of the design so you can have a controller hundreds of meters away from the thing you want controlled and as long as there are a couple of devices on the mesh between them it will work. We've seen how great WiFi repeaters are... plus WiFi on battery is basically a deal breaker, whereas you can have z-wave devices last two years on some AA batteries.
Z-Wave and Zigbee are both so much better than WiFi at automation that I can't even fathom why someone would suggest the opposite.
That being said, some combination of BT/LE/Mesh + WiFi and/or some other networking protocol would probably win very quickly if it wasn't encumbered with large licensing costs.
I refine my comment to capture BTLE as one of the protocols going forward, in addition to wifi.
Z-wave is a proprietary protocol. Only 1 company has the IP & monopoly on manufacturing Z-wave chips... By contrast, any of these other techs are open and have multiple implementations available from multiple manufacturers.
Z-wave's biggest short coming in my opinion is how easy it is to overload the network. Turning off 40 lights at once has half of the operations drop off due to the network getting overloaded and just dropping commands. If you have a few devices reporting their power usage, the network becomes quickly overloaded and you get the same command dropping crap in even simple operations like 'turn on light 2 when light 1 turns on and vice versa'.
I have a condo with z-wave everything right now, but after seeing how much of a mess all IoT home automation crap is, I'm going to sit and wait until we have something that works properly that doesn't cost $60-$100 per light switch or require maintaining something complicated.
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IMO we should have a dual network solution. Something like wifi for plug in devices which also act as repeater networks for the battery powered BLE sensors and such.
But it's dated (from the 1990s), there is zero encryption/authentication, and devices are kinda expensive.
I used to use insteon in a small test build out, but got frustrated with their bad software support. You have to use a ~$300 hub with a $80 PLM modem before you can get something half decent. And Insteon devices having a reputation of breaking after a couple of years due to using cheap capacitors and such put me off from using it any further.
I'm cautiously optimistic for Bluetooth Mesh giving z-wave a run for its money but its still very early days.
A remotely controlled plug should be running tens of kB of firmware, at most, and that includes crypto libraries. It shouldn't be running the megabytes of code that an embedded Linux OS represents.
Yuck.