I have exactly the same question: Does anyone use the USG Box in combination with the Sunrise Internet Box (copper)? I would like to operate the SIB in bridge mode or at least use the VPN site-to-site function from Ubiquiti.

I have both the USG and the USG Pro in use, with init7 1GB fibre. With the USG Pro you can connect directly to the fibre using an SFP module, this is not possible with the USG. I'm not sure if this is possible with Sunrise or if there is a requirement for the box, with init7 it's not a problem.

The USG Pro manages full 1GBit, the USG not the full bandwidth. If you switch on the IPS firewall filters, the performance drops significantly. If you plan to use the IPS, I would recommend the USG Pro (which has a loud fan) or the new UDM Pro, which also integrates the Cloud Key. If you only use the USG as a router and as a VPN server, then it should easily be sufficient...

I used the box with Init7. It does 1 Gbit easily, so it has enough power. VPN is also OK with 50 Mbit. However, I don't know if the limitation is due to the smartphone or the USG. Highly recommended, reliable and easy to use if the admin software is installed (on my NAS).