I bought this usb-c hub a few weeks ago and been using it since. To my point in the title, it works great when I plug in my monitor via HDMI to extend my macbook pro screen. The 2 usb-a port works perfectly as charger when I connect my iPhone to it.
But when it comes to data transfer, it is not as smooth. After I plug my iphone via usb-a-lightening cable, I see "Trust this computer" alert on my iphone popping up again and again and again. The connection is not very stable and drops frequently due to the same reason.
SD card slot works fine expect that sometimes macbook pro can't detect the storage after it is plugged in. I just unplug and plug again to get it work. This is not big issue given the price of this item.
Haven't tried external hard drive via usb-a yet so can't comment on that. (will probably update if I got a chance to try it)