…ha! - that is a question i just answered today on the LZX-website:
…as dongles i use USB3-dongles branded HAMA (a well know german brand) which convert up to 4K-input to 1080p output - or whatever you need…
…i also use the Elgato 4K-dongle, but this one gets really hot in use, is lagging and sometimes crashes…
…and i have a couple of the ‘good’ no-name dongles for around 10-15€ which work really well…