FYI, ITead has announced in a video that they will soon sell a Sonoff branded Zigbee 3.0 USB Dongle that is based the exact same Silicon Labs EFR32MG21 SoC as their Sonoff ZBBridge Zigbee Bridge
Note! Ember USB Zigbee adapters/dongles/sticks like these are highly recommended over using a remotely connected Ember module using a serial-to-ip bridge / serial forwarding server like ser2net. The reazon for this is that clients using the EZSP serial protocol requires a robust connection between the EmberZNet Zigbee stack running on EFR32 MCU and the serial port of the Zigbee radio. With solutions such as ITEAD Sonoff ZBBridge or a Ser2Net serial proxy connection over a WiFi network it is expected to see NCP entered failed state. Requesting APP controller restart in the logs. This is a normal part of the operation and indicates there was a drop in communication which caused packet loss to occurred between the zigpy radio library and the Zigbee radio. The use of serial network proxies/bridges/servers over WiFi is therefore not recommended when wanting a stable Zigbee environment with Silicon Labs Ember based Zigbee radios. The developers of the bellows radio library for the zigpy project has more information about this if needed.