So I just got an Elgato Thunderbolt 3 dock the other day for work and I have some impressions and information I want to share.
I have two Dell P2715Q monitors (4K @ 60Hz) and was driving these on my 2016 15" Touchbar MBP via USB-C to DisplayPort cables from Startech without issues. When I got the Elgato I was able to use one of the existing USB-C cables on the monitors without issues and got full 4K @ 60Hz however on the other monitor when I switched to a pure DisplayPort cable I was getting a black screen or flickering every so often but MacOS was able to identify the monitor just fine. No matter which monitor I tried the issue carried with the pure DisplayPort cable monitor so I know it wasn't the monitors. These Dells also have a mDP port and came with a mDP to DP cable which I tried on both with no luck as well. The Dells also have a feature called MST which allows one monitor to drive two monitors via a single cable to the device and then a DP cable between them to carry the signal. On the second monitor in MST it puts the DP port to 1.1 therefore only allowing 4K @ 30Hz MAX. So I kept one dell attached with the USB-C to DP cable and the MST mode off making it 4K @ 60Hz and then enabled MST in Secondary mode therefore turning the monitoring into DP 1.1 and the signal came online with either DP to DP or mDP to DP cables.
Everything else on the dock worked fine such as ethernet, USB, audio, FULL 85-87W charging, etc. but I have this nagging display issue.
According to Elgato's documentation it is capable of dual 4K @ 60Hz so I've spoken to support last night and they have escalated to development for investigation.
Just an FYI if anyone is considering this dock.