The Dakota is a gear calculator - it uses engine speed (tachometer signal) and vehicle speed (speed sensor signal) to determine gear after you've programmed it. This means that it isn't useful for the one thing I find most important about a gear indicator - making sure you're in 1st when stopped. The Dakota shows "0" when the bike isn't moving.
The Air Rider, Owl, and Dave's Cycle gear indicators make use of the gear position switch on the GL engine. It provides ground on different wires for all gear positions except 1st (if no ground on any signal wire then assume 1st gear). This means no programming and an accurate indication regardless of speed.
The Air Rider unit is nice if you can use the one that goes in the panel below the right pocket (non-nav bikes) but the one that replaces the left pocket door with a cheap panel isn't something I'd want to have on my bike. The Dave's Cycle indicator is very nicely designed (I have it on both 1500s) but I don't like the way the 1800 version blocks the upper portion of the speedometer. So, I guess I'll be getting the Owl version as soon as I can get permission from "she who must be obeyed".