QMTL via Amazon offers the Tacklife Outlet Power Tester for $9.97. Coupon code "74HAQDOT" cuts it to $5.98. Plus, Prime members bag free shipping. That's $17 off, tied with our mention from last month, and the lowest price we could find. It features three indicator lights and a nominal frequency range of 50Hz to 60Hz.

Update: It's now $8.97 before coupon code "74HAQDOT", $6.01 after.