I don't own any freelights, though one of my friends has some, which is how I know about them.

Can I compare them ?

Yes, easily.

Freelights are a set of blinky LEDs that require no batteries (more similar to Reelights)

Down Low Glow System is for people who want to pimp their ride...oh and it is battery powered...
* you’ll hear people shouting “Nice bike!” and “Your bike is tight!”
* weighs over 1lb !! (and that's just the battery)
* The Down Low Glow is the only bicycle safety light with GSR (lol)

I'm not totally convinced this is good advice either: "as you sprint to catch a yellow light, knowing that cars in the opposing direction will wait until you cross the intersection" - not something I would bet my life on tbh