got it from trashing tech in ship swapping. So what is it good for?

Plenty in caves i sell them they make good money and sentinels don't react when picking them up so easy to make money.

There some blue prints that need cubes but ive not use them yet.

That is... not universally true. On most of the planets I've seen that had vortex cubes (or graviton spheres) on them, I got an elite sentinel squad (two normal sentinels and one of the dog-like robot version) every time I picked one up.

Thats a forum for so others can reply with different experience i encounter 3 worlds with vortex cubes and was never attacked by sentinels.

Now because of your reply we know you can be attacked also which is not a real pain only some annoyans.

I kept so many things for SO long because I wasn`t sure if they`d be really useful later, handicapping myself.

Now I just sell them and find another one later.

Sell it. They are a commodity. And yes, there are both alert and no alert sentinel planets, find a cave, take them all...sell...repeat! Gravity Orbs are good too...but they ALWAYS alert the sentinels.