One of my favorite floaters for a shrimp tank. You do have to get rid of the "old" part before it starts to shed the needles every once in a while. I would have some in my CRS tank that would be 2 feet long after a couple of weeks. I'd just pull off the newest 6" or so and throw the old stuff away.
It's not guppygrass, it's hornwort. There does seem to be two different kinds though. They look exactly the same, but one would always get bigger than the other, even in the same tank. I got them from different sources, maybe one was just genetically different? From the pic, your's looks like the smaller one I had?
Hornwort will send out some roots, not many though. Guppygrass sends out more roots more often and the leaves look more like, well, grass