Originally Posted by
Koyote
Totally worth the small cost. You'll also get a Di2 battery level readout on your Garmin, as well as a gear position indicator. The latter is surprisingly useful if you live in a hilly area: when you're on a really steep climb, a glance at the computer will indicate whether you still have a bailout gear available.
Do you have a Garmin without touch screen or something? It's at least as easy to change pages by swiping to either side as it is to find a button.
I love having the battery % and not having to screw around with a color coded light under my stem.