Yeah, it doesn’t really work like that. 
I’m trying to figure out the best way to put this without writing 20 pages.
First of all, Z wave and zigbee are different protocols, each running on their own network. The hub is a plastic box that includes a controller for Zigbee and a controller for Z wave, but the networks themselves are independent. Zigbee repeats only for zigbee and Z wave repeats only for Z wave.
Both zigbee and zwave are mesh networks. That means that there is one primary controller (the one inside the hub). All of the N devices get added individually to their primary controller, and have a network ID on that controller’s network. In zwave, The hub will assign the device ID and tell the end controller what it is. In zigbee, each device comes with its own ID which it tells the controller at the time that it joins the network.
For both, almost all mains Powered Devices can act as a “repeater“ to pass along the messages of other devices. This allows each individual device to be very low power, which is why they are so good for battery powered Sensors. Zigbee, for example, a typical device can only transmit for about 40 feet. But as long as that message reaches one of the repeating devices on the same network, it can be passed along, pony express style. Until eventually it reaches its destination. This is where you can have a network which can cover a four-story house. 
So most light switches, relays, plug-in sensors, even lightbulbs, etc. are all repeating devices.
Most battery powered devices don’t repeat just because it would use up too much battery life.
The IKEA extender is sold specifically for use with their battery powered shades. You don’t need it in a typical home automation set up. And it’s actually a pretty low powered extender anyway. Just a regular IKEA plug-in smart plug, the $10 one, will work fine as a zigbee repeater and actually has a little longer range than the Single purpose extender device.
The repeating function is handled automatically by the network. All you need to do is add a device to your network which has the repeating capability, and it will automatically do so as needed. Again, this is true for both zwave and zigbee.
So start by reading post 11 in the following thread, then go up to the top and read the whole thing. That should give you a better understanding of how mesh networks work. ( The topic title is a clickable link. I’ll link directly to post 11.)
So in your case, you probably don’t need the extender device at all. Just a few of the smart plugs. And just add everything to the network, adding the repeating devices first, then the battery powered devices, and the repeating function should work automatically.