I own Ikea Tradfri lamps and controllers, currently. I’d like to buy more smart things from other manufacturers (e.g. for controlling radiators, etc) but each and every manufacturer has its own (costly) bridge. I don’t want to buy and use X bridges.
I own a RPi 3 with OH2 installed and running (planning on upgrading to RPi4). I am currently thinking about buying a zigbee and/or zwave module for the RPi. Is it possible to integrate smart things directly without buing/using several bridges if I add a zigbee (for Tradfri) / zwave (for other smart things) module to the RPi?
Can you recommend zigbee/zwave modules for the RPi3 (and RPi4)?
Z-Wave is designed for interoperability. Instead of buying a module for the Pi it may make more sense to buy a USB stick controller. You are then able to position it on a cable to increase range. It would also permit you to move to a different server. I am migrating my OH from a Pi to a Debian VM on a server.
Where are you located? Z-Wave hardware is region-specific due to frequency differences.
Why zigbee2mqtt instead of our excellent zigbee binding? I avoid Zigbee because it uses the crowded 2.4GHz radio band. This question really should be a new thread though.
@sihui is in Germany running many devices. I will let him advise.
My old USB controller for North America did both Zigbee and Z-Wave but that is unusual. My new controller is Z-Wave only.
You may need 2 separate controllers but our developer for Zigbee and Z-Wave is one of the most dedicated I have seen.
There is no general answer to that.
Example: most Xiaomi sensors are working with the zigbee binding but are not compatible to 100%.
Also Hue is mostly compatible, but not all devices.
You need to find out (through the forums search) your exact device if it is working or not.
Also on the bindings pages you can find devices tested to work with the bindings:
Mqtt is a very light weight, I use this most all my automation, four people in my house (2 of them teenagers) constently using wifi connection and no issues. I have the coordinator located in a central location, home is approx 4000sqft, and a single stick covers everything.
The other reason I recommend looking at zigbee2mqtt is the amount of supported devices. You can look here at the list of supported devices. Also check at the top of the page to see how you can add a device that’s not already on the list.
Not trying to disregard the zigbee binding, only putting it out there so you can make the best choice for your setup. If interested here is a link that takes you thru whats needed and how to set it up. https://www.zigbee2mqtt.io/#getting-started The info under getting started is all you really need for it to work with OH.
No interference from microwave ovens or wireless telephones? There are so many devices using that unlicensed band that 2.4GHz Wi-Fi here at a University is not dependable and only offered with limited support.
Nothing that I’ve noticed and have been using for over a year.
If the OP is looking to use this in a large environment such as a University then you are dead on about interference issue. Thanks for mentioning this and I will add this caveat to an future recomendations.
I recently got the deconz shield for the Pi (dresden elektronik). Using Philips hue and xiaomi aqara at the moment.
It’s not plug’n’play. But got it working using the beta-firmware.
Internal rechargeable then as it has power when removed… shows how much I’ve had to touch it
Original question was for both so thought I’d recommend the Zwave side of things
I’d like to spare myself the hassle of flashing a CC2531. So, if I buy and use the ConBee2 it only works with the deconz binding, right? Does this need the deConz software installed in order to work?
At least its a definitve answer 
for zigbee2mqtt.