600Mbps Dual-Band Wi-Fi USB Adapter - 2.4GHz and 5GHz, 802.11ac

The 5 GHz band is the reason to buy this one over the cheaper single-band adapter beside it. A crowded flat has a dozen networks fighting over 2.4 GHz; 5 GHz is usually empty by comparison, and on 802.11ac it carries far more data over a shorter range — which is exactly the trade you want in the same room as the router.

It is a nano dongle: it goes into a USB port and effectively disappears, so a laptop can stay in a bag with it fitted. Eight dollars to give a desktop with a dead Wi-Fi card or an older laptop a modern connection.