I went with the Gearingo gear indicator.
Gearingo Gear Indicator It attaches to the handle bar. It plugs into the diagnostic plug under the seat. Here is how they describe it. I like it a lot.
Fast and Accurate
The indicator is always correct and displays the gear without any delay, including when stopped and skipping gears. The Gearingo was designed to take advantage of Triumph's advanced technology, and displays the gear information from the motorcycle's built-in gear position sensor located in the crankcase.
Plug & Play Install
Secure the Gearingo either below or above the handlebar with two screws, route the cable to the side panel or under your seat, and then plug the attached cable into the diagnostic connector. The indicator does not need to be calibrated like old-fashioned units, you don't need to watch an installation video, or modify your bike in any way: plug it in and ride.
Auto ON/OFF
The Gearingo communicates with the ECM module allowing it to turn on and off automatically with the ignition key, there are no switches or buttons to press. The Gearingo has a unique micro power design making it always ready for you to jump on your bike and ride.
Display Battery Voltage
Do you worry about your battery, wondering if it's time to put it on a battery tender? Every time you turn the ignition key on the Gearingo will accurately display the battery voltage, and the Gearingo can also warn you of a low voltage when you turn the key off, to make sure that you never forget to charge your battery.