The GO-510-UN rivnut/threaded insert tool is the best on the market in terms of quality and price point.
It comes with long arms to make installing larger sizes easier, and has soft rubber grip handles for operator comfort. It can install threaded inserts from 1/4-20 up to 1/2-13.
Type Lever Style
Thread Type UNC/Metric
Use With Internal Thread Size 1/4-20, 5/16-18, 3/8-16, 1/2-13, 6mm, 8mm, 10mm
Application For Setting 1/4-20, 5/16-18, 3/8-16, 6mm, 8mm, and 10mm Rivet Nuts and Nut Inserts
Includes 4  Nosepiece and a variety of threaded inserts and a Service Wrench