A few weeks ago I went ahead and installed the Mercury SmartTachs in place of my analog tachometers.
This has to be the best bang for the buck upgrade I've done. The information they provide and allow you to scroll through while underway is great!
Before
After
It took less than a half hour to install. Remove the analog tachs after you remove and tape up the old wires. The junction box for the SmartCraft is right behind the chartplotter.
Remove two caps, and plug in each tach. When they are first powered up you will have to assign each to port or starboard, and then roll through the setup of what menus you would like it to display.
The instructions also state a dealer will need to plug in their CDS tool to program each engine position, to either port or starboard. I did not notice any change after I had this done.