Essentially, one that gives the ability to break down your gun to fit in a brief case. Decreasing bulk and difficulty to hide it, but at the expense of needing to spend time assembling it to use it.
So yes, the Sniper Rifle mod. We see this a couple times in The Clone Wars series.
But it especially makes sense as something useful for the Rebels who might (even more especially, a Sniper Spec!) want to go and snipe off an Imperial Officer, but it can be really hard to sneak a rifle around, it's the perfect thing for the Sharpshooter on the go!
And obviously this one makes a ton of sense for Edge too. A few different concepts it could work for.