My main switch a netgear WAX 206, also only has one 2.5gbit port, I assume its to allow multi gig internet services. Whilst you would not saturate it from one device (which personally I think is a very good built in form of QoS), you could do it via multiple devices at same time.
The device, I think is to provide some funds to the OpenWRT project, hopefully it doesnt end up in future years where they only support official OpenWRT devices.