This is the easiest way to build a "TuneRite".
All you need is an electrolytic capacitor, a resistor, the plug for the tuner connector and a few inches of wire. Pressing the Tunebutton for about 3 sec switches the TRX to TX at an output power will be less than 10 watts. After approx. 8 seconds, the icon switches back to receive.
I was able to test these simple TuneRite on the ic7400 / IC746Pro and the IC706MKIIG.
About experiences with other Icom devices, check the Web. You can write me your experience and sent a mail to dj1fc@darc.de.