Shimano Di2 gear display

The e-tube software is free. I run it on a laptop and plug it in via the di2 charger to my junction A.

Setup this way is foolproof and simple. Alterations, firmware updates (did one last night and charged my di2 battery were straightforward and quick. I don't bother trying to do that lot via the app on iPad or iPhone wirelessly as it is more clunky.

If you already have a Garmin you will be familiar with setting up data fields on various screens. All you do is touch and hold the field and it will open the menu to choose what you want to display. With the Bluetooth sender unit in your di2 circuit somewhere you will be able to select di2 fields including 'rear gear', which I have displayed at the top of my 'home' page - the one that I have displayed most of the time on a ride. Like this;

Another bonus of fitting the Bluetooth sender is that you can program your di2 'hidden buttons' to scroll the pages of your Garmin, which I really like.

PP

I'm on a Mac and really cba to partition just for Shimano. Luckily I have a friend with a laptop dedicated to the Shimano software

I have a Mac as well and run a Windows VM with the eTube app (using VMware Fusion but Virtual Box will also work and it's free). I used it to recover a "bricked" Di2 system that failed during an upgrade via Bluetooth over the iPhone app.

As stated, once you have it setup, it's VERY easy to configure. In fact, as soon as you connect your Di2 to the Garmin via ANT+ (or Bluetooth, but don't recommend this), you can configure the buttons from the Garmin. Each button has three functions; short press, double press, and long press. I have it setup for: Short press left side, Page Up, Short press right side, Page down. Double press left side, Lap screen (my main screen), Double press right side, Elevation profile. Long press left side, Group track, I don't remember what the long press is set for on the right side... [cheeky]