So, we all know about this particular upgrade:

in a vacuum, it doesn't sound awe inspiring - secondary weapon turret, 3 dice, range 2-3, Perform this attack twice, each time this attack hits, deal one damage and cancel all results.
So, they're capped at 2 damage per turn, over two shots, with no chance for critical hits, useless at range 1. Doesn't sound too powerful at all, does it?
In fact, it's probably one of the most consistently used upgrade cards since it's release. Back in Wave 6, secondary weapon turrets weren't up to much. The Blaster Turret was the subject of ridicule, the Ion Cannon Turret wasn't seen a great deal and the Autoblaster turret hadn't found it's Ghost niche. The TLT changed all that. Suddenly, secondary weapon turrets -and the ships that carried them - became a thing. And they haven't really gone away since.
It's tempting to say that TLT's success rests upon the perfect storm of upgrades and abilities. Certainly, the way it's currently being exploited with Kanan/Fenn requires a fair bit of interplay. Miranda's ability works well with it, and obviously BTL-A4 Stressbot TLTs were another example. But then again, we had the death of a thousand cuts from Thug Life builds (and occassionaly HWK equivalents). the arrival of the VCX, TIE Aggressor and Scurrg means there's more ways to put it on the table now, and it's consistently doing well.
And I think consistency is the right word here.
When I first saw the upgrade, I immediately thought it would be a way to reliably chip health away from low agility, high mitigation targets. Looking at you, Fat Han with your Evade token and C-3P0. But it's proven to be equally effective against high agility, low health targets. Low agility ships resign themselves to soaking up the damage. Dedicated arc dodgers struggle to avoid them, and high agility eventually fails you when enough shots are coming in.
TLTs are essentially an all-purpose can opener - easy to use, reliable and effective against pretty much everything. Is that a good thing, or not?