Here’s the link:
Here’s a relevant discussion thread:
I don’t think you’ll be disappointed. I bought several from Itead, but the price has gone up a few dollars: https://itead.cc/product/sonoff-zigbee-3-0-usb-dongle-plus/
Edit: if you’re using windows, go to windows update/check for updates after plugging it in to your usb. The correct usb driver for it should show up to install. I used the TI software to do the firmware update (it’s also free). You’ll want to take the case off of the dongle until you have it updated and paired with Hubitat because the buttons you’ll have to press are on the board.
Firmware flashing: