The SIIG Dual USB-C Hub with Card Reader and PD Adapter provides an option to expand your Mac's connectivity but note that it only caters for 13-inch or 15-inch Mac's supporting two USB Type-C/Thunderbolt 3 connectors or more. The hub has two adjacent USB Type-C connectors affixed on one side to attach to both Thunderbolt 3 based USB-C ports on the Mac. The other side of the hub provides one Thunderbolt 3 port and one USB 3.1 Gen 1 (5 Gb/s) Type-C port to connect to a USB PD power adapter, external display or USB Type-C storage drive.
Given the hub doesn't actually have any Thunderbolt or USB PD chip inside, it only uses a simple approach to support charging over USB Type-C without having to use active USB Power Delivery negotiation as well as 4K or 5K video output and USB 3.1 Gen 2 (10 Gb/s) speeds. When attached to the Mac, the hub just passes USB Type-C signals through one of the two Thunderbolt 3 ports on the Mac, while converting the other Thunderbolt 3 port into a USB 3.1 Gen 1 (5 Gb/s) Type-C port and card reader.
We picked up the SIIG Dual USB-C Hub with Card Reader and PD Adapter on a recent trip to Fry's Electronic USB-C Products.
The SIIG Dual USB-C Hub with Card Reader and PD Adapter claims to pass through charging up to 87W for the Mac using USB Power Delivery 2.0 technology when connected to a Apple or compliant USB PD based power adapter through the hub's Thunderbolt 3 port, or up to 4Kx2K@60Hz or 5K video if connecting to a supported Thunderbolt 3 display or transfer data at USB 3.1 Gen 2 (10 Gb/s) rates. The other USB Type-C port on the SIIG Dual USB-C Hub with Card Reader and PD Adapter as well as the two additional USB Type-A ports just support USB 3.1 Gen 1 (5 Gb/s) speeds to connect to USB peripherals.
The hub also has a card reader which allows SD, SDHC, SDXC, MMC, MicroSD or TF memory card with max 2TB storage to be used.