I kind of think that gem destabilizers might actually be old tech. Though when the image of what appears to be Pink Diamond holding what appears to be gem destabilizers appeared, I was quick to dismiss them as being anything close to destabilizers. Gem destabilizers were era 2 tech, and so they couldn't have possibly been used by Pink Diamond.
But the reason I thought gem destabilizers were era 2 was because of Garnet. If Garnet had known of them, she would not have acted so rashly, just rushing at them. Especially after Jasper had literally announced, “prime the gem destabilizers.” It wouldn't fit the rational gem with future vision.
It would, however, fit the gem who constantly freaks out whenever Homeworld is involved. When she discovered Lapis was still conscious in her mirror, she first tried to deny it -- “it’s just a mirror; a tool. It can't want anything” -- and then tries to get Steven to give the mirror to her so she can bubble it. She breaks the warp pad after Peridot’s first trip to Earth. After they capture and bubble Peridot, Garnet calls Peridot’s words “the desperate lies of a gem that's been caught.” Homeworld gems so freak her out that a mere tech is enough to unnerve her.
And then there's Steven’s Dream. It would have been so much better if Garnet had said, “Steven, Blue Diamond is on Earth. Once she leaves, you can visit the palanquin. But now, it's too dangerous. So please stay home.” But she doesn't. She freaks out, and panics. The mere idea of Blue Diamond upsets Garnet so much that she is unable to act in any way other than panic.
So I can see a similar situation happening in The Return. Not only are there Homeworld gems, but one of them fought in the war and is actively antagonistic. And right before she took out the gem destabilizer, Jasper said, “Yellow Diamond needs to see this thing.” Yellow Diamond might not be Garnet’s Diamond, but she's still a Diamond. So, with all that, it makes perfect sense that Garnet would launch herself at Jasper, not even paying any attention to the gem destabilizer itself. Jasper wanted Steven and Garnet couldn't let that happen. In her desperation to save Steven, she lunges forward, not once thinking of the consequences.