Totally independent system to provide redundancy for de-orbit in case control to the main satellite is lost, which is a problem.
today we count something close to 1700 active satelite and dubling this number in a year (and maybe again the year after) it is a step that have to be done right, the first time because space is big but the good orbits are few; and a kessler syndrome scenario is possible. It is imaginable that to keep the whole carousel running, you need to be able to launch and dispose satellites quickly and safely.
And even though tethers are not exactly the quicker or safer system, there is a lot of work to be done and is interesting that PSLV C-38 launched many deorbiting devices.
Also, many satellites are not deorbited. Most satellites in medium to high orbits, especially those in geostationary orbit, are moved into graveyard orbits near their end of life when they are still operational, but they lack sufficient propulsion to deorbit or bring their perigees low enough for their orbits to degrade in a meaningful amount of time.
The point of this experiment is to test out a device that doesn't add significant extra mass to a satellite but would be able to deorbit it in a timely manner after it has reached the end of its usefulness. This would be a big step in keeping Earth orbit clean from space junk and is a worthy research endeavor, especially considering the low costs involved.
We also already use "de-orbiting" systems in real satellites: we just burn their remaining fuel in the RCSs to either push them back into space (the normally talked about junk cloud) or we pull them into a decaying orbit (what already happens with CubeSats). The only reason this is done in the big-leagues is because the average "normal" satellite is about the size of a small car.
A CubeSat will effectively be taken out by gravity/drift very quickly (most missions are 2 months to 2 years) and it is perfectly safe to do so.
I don't see how this is a "Space Junk Solution" and from the article:
> "The planned demonstration is an important milestone to develop and promote the use of this technology," Krag told Space.com. [Space Junk Explained: How Orbital Debris Threatens Future of Spaceflight (Infographic)]
1. This is already something we do
2. This is no needed in CubeSats