The SLZB-MR4U: Why a Multi-Radio Zigbee and Thread Stick Is a Smart Home Upgrade

If your home automation journey started like most, it began with a cheap USB Zigbee stick plugged into the back of your Home Assistant server. It works — until it doesn't. Radios wedged next to USB 3.0 ports, SSDs and Wi-Fi antennas share a cramped corner of the house, and the mesh has to reach every room from wherever the server happens to live. SMLIGHT's SLZB-MR4U takes a different approach: a multi-radio coordinator that treats Ethernet, not USB, as the primary interface — and throws in a second radio for Thread and Matter while it's at it.

What Is the SLZB-MR4U?¶

The MR4U is the top model in SMLIGHT's MRxU family, a series of five Ethernet-attached multi-radio coordinators that share one body, one set of ports and one firmware, differing only in the radio chips inside. The MR4U pairs a Texas Instruments CC2674P10 (Radio 1) with a Silicon Labs EFR32MG26 (Radio 2) — the premium "P10 + MG26" combination. Both radios support Zigbee 3.0 and Thread, and both run simultaneously on separate channels: Zigbee on one SoC, Thread on the other, with no mutually exclusive network stacks.

The device measures 160 × 24 × 28 mm, weighs 86 grams, and carries two rotatable +5 dB antennas. Power comes from either USB-C or PoE (802.3af, 48 V) — an isolated transformer keeps the two power paths separated, so you can even feed it from both. The brain is an ESP32-S3 core running SMLIGHT's SLZB-OS, with a hardwired WIZnet W5500 Ethernet PHY for a deterministic network link.

The Radio Where the Mesh Needs It¶

This is the core argument for the MR4U — and really for the whole MRxU line. A Zigbee coordinator that lives inside a server rack is a compromise: USB 3.0 ports are notorious for interfering with 2.4 GHz radios, and the server's location is dictated by cabling and cooling, not by radio coverage. With an Ethernet-connected coordinator you can put the radio where the mesh actually needs to live: in the centre of the house, in the attic, the basement, or a network cabinet — anywhere a Cat6 drop reaches.

PoE makes this genuinely painless. One cable delivers both data and power, so there is no wall wart competing with the antenna for space. Move your Home Assistant server, change providers or rebuild your rack, and the Zigbee mesh stays exactly where it was. For Zigbee2MQTT and ZHA users nothing changes in the software stack — the stick simply connects over TCP/IP instead of a local USB port.

Two Radios: Zigbee and Thread at the Same Time¶

The second radio is what sets the MR4U apart from both classic USB sticks and SMLIGHT's own single-radio units. With Matter-over-Thread devices entering more households, a growing number of people end up running two networks: Zigbee for the existing sensor fleet and Thread for Matter devices. Normally that means two coordinators, two USB ports, and two pieces of software to babysit. The MR4U runs both stacks from one device, on separate channels, with the ESP32-S3 core orchestrating them.

Home Assistant's own SMLIGHT integration recognises the device natively, and the unit can act as a Zigbee coordinator or router while simultaneously serving as a Thread border router. The two antennas are individually rotatable, so you can optimise placement for both 2.4 GHz networks at once.

A genuinely clever extra is USB passthrough: plug any CP210x or CH340-based dongle into the MR4U's USB-C port and it becomes available over the network. That means a Z-Wave stick, for example, can hang off the MR4U in a central location and be used by Home Assistant as if it were plugged in locally — handy when you want Z-Wave, Zigbee and Thread radios all in one physical spot, or when your server is a VM or a container without reliable USB access. In the Home Assistant community, users are already running exactly this setup: PoE-powered MR4U with Zigbee on Radio 1, Thread on Radio 2, and an external Z-Wave stick passed through the USB port.

Firmware Freedom and Local Control¶

SMLIGHT ships the device pre-flashed with SLZB-OS, so it works out of the box — no flashing cables, no toolchain, no late-night tinkering. The web UI handles configuration, diagnostics and over-the-air updates for both radio SoCs, so you never need physical access to update the coordinator firmware. For the more adventurous, one click reflashes to ESPHome, community firmware, or back to SLZB-OS, and SMLIGHT publishes an open-source, MIT-licensed core firmware as a lighter alternative.

Local-first is the theme: nothing requires a cloud account. SLZB-OS even bundles WireGuard, which makes for a fun topology — run the Zigbee and Thread mesh in a second building, and reach it from your Home Assistant server over a single VPN tunnel, as if the radios were in the same room.

Real-World Experience and Caveats¶

The hardware has been tested in the wild since the unit started shipping earlier this year. The Haade.fr review from March 2026 sums it up bluntly: "it works like a charm" — with Zigbee and Thread coexisting without drama. One caveat worth knowing before you buy: reviewers at SmartHomeScene point out that the EFR32MG26 offers no tangible Zigbee performance benefit over the EFR32MG24 used in the cheaper MR3U, since the TI CC2674P10 does the heavy lifting for Zigbee. The MG26's advantages — Thread 1.4 and double the RAM — matter mainly if you plan to push the Silicon Labs radio hard. If you only need Zigbee, the MR3U gives you the same main radio for less; if you want the premium pairing with the most future-proof Silicon Labs chip, the MR4U is the one.

The Verdict¶

For anyone who has wrestled with a USB Zigbee stick jammed behind a server, the MR4U is a quiet revelation: rock-solid radio placement, one cable for power and data, two networks from one device, and firmware you control without a soldering iron. It is not the cheapest coordinator on the market, but it solves a class of problems that cheap sticks simply can't — and in a smart home, radio placement is worth a lot more than a few euros.