has the Edimax EW-7822ULC AC1200 Wi-Fi USB Adapter with MU-MIMO for $14.99 with free Prime shipping.
This could be a good way to upgrade the Wi-Fi on your devices to take advantage of MU-MIMO support in your fancy new router. In order to see any benefit from MU-MIMO, you need at least two clients that support it. This would be a good price for the specs even if it didn't support MU-MIMO.
Edimax is the manufacturer of the identical ASUS USB-AC53 Nano which costs more than twice as much.
Edimax Product Page [edimax.com]
WikiDevi entry for hardware info [wikidevi.com]