I don't know where you got the LEO restriction from. All of the Planetary Society pages are clear that this LEO test is a test, and the real deal is above LEO.
It's not a restriction for solar sails. I know that.
But the grandparent comment said "It's mainly targeted at cube sats".
And cubesats tend to be LEO-based. (They tend to be the cheapest thing possible - and its harder to get into a higher orbit. And they tend to be launched parasitically to boot.)
They're hoping to enable cubesats (or at least small sats) to do deep space or planetary missions by proving a low-mass and low-complexity propulsion system.
There's enough atmosphere in LEO that I am surprised that it's a net positive, frankly. I mean: the ISS requires a reboost every few months.