The Shadows would be an interesting discovery for the PCs to meet up on in the Great Rift, either accidentally or while doing research.
They look like they belong there, too, depending on how cinematic your Traveller universe is.
Naturally, you can combine this with the Element Class cruiser set, as the Navy is quite interested in reports of lost, active Ancient military tech in the region, and has sent a warship to investigate.
Now, whether the Shadows are really Ancient military technology is left for the Referee to decide.
I’d put them as solitary “deep sea” space lifeforms myself, as ugly as our own fish in the deepest ocean trenches. They are designed to feed on something (space whales?) or even hiding from something, and rarely venturing from their natural starless, deep void habitat. Also, they’d be very rare, perhaps one per Great Void sector, and none in the Lesser Reft where
I live the Empty Quarter is located.
The real problem, storywise, is the those Battlecrabs with their Ginsu Beams that never miss are way overpowered for the Traveller setting. Now, that’s OK: life often isn’t fair, and warfare is generally unfair as well. But the Referee generally wants his PCs to feel victorious after a tough fight, and that isn’t going to happen here.
At least, not without some upgrades: disintergrater spinal mounts, say.
And even this at best gives you offensive punch, turning your ship from a scrap pile in waiting, to a glass cannon. “You can dish it out, but can you take it?”
Still… an Imperial Navy “Special Circumstances” unit, created to handle very special problems like this, would be interesting to contemplate.