Any reason to add another quality instead?

Not if the item you're using it on is a weapon that has Auto-fire.

I don't think it's RAW, but using it to reduce the Threat cost of activating refined Cortosis (to short out sabers) might be kinda cool too.

Well depends on your play style

add damage on an Lightsaber,

reduce link cost on a two blade Lightsaber or a two-barreld gun.
reduce crit cost on the sniping rifle,
reduce the cost for concussive on a brawl weapon,
reduce the Cost for Stun for not lethal attacks
increase vicious or pierce (as long as the weapon already has this option)

or the by Happydaze reduced costs for refined cortosis (so I also have to read the full text for Jury-Rig if it is only for advantages but I believe it says only cost...)

to be honest the auto-fire option is just plain damage, quite boring and totally broken (to me at least) but as long as your GM don't set a stop sign to it, it is the mostpowerfull (in raw damage and mowing down minions)

So I play a refluffed shistivanan as a tusken Trailblazer.

243321 thinking of cross spec-ing into gadgeteer.

Wanted to eventually get the model 37(I think that's the number).

I basically want a boom cannon Long gun. So mostly I'll be using the detonator rounds for raw damage. I'll get disorient from trailblazer eventually.

the model 38 sharpshooter? well I'd go for the Crit then, thanks to the accurate 2 you'll gain 2 Blue Dice wich will increase the likly hood of crits happening even more

If you have two ranks, twin SSB-1 Static Pistols can be extremely nice. Four advantage to deal 16 unblockable strain damage, and you can put on laser sights to get two of those automatically.

A Saboteur/Demolitionist with Jury Rigged and Master Grenadier can rig up their Model 38 (or any other Blast weapon) with detonator rounds to blow up on one advantage even if you miss. Especially if you have lots of Powerful Blast ranks, you end up with an Extreme-range weapon that only needs 1 advantage to deal 10 damage.

The flechette pistol is also nice for this, bringing the cost of Guided down to two advantage.

Low damage, high crit is a great way to play non-energy weapons.

And the model 38 has more than enough hard points to make things interesting!