I don't know Nitrux, but Zorin Lite is my daily Linux right now. The "full" Zorin is not free, but the Lite and educational versions are. It is based on Ubuntu, and I would guess that it would run very well on your laptop, even from USB.
There are hundreds of different Linux, but they are really all quite similar with a few exceptions... like how they manage "packages"... that is, how they update their software. Debian (.deb) and RedHat (.rpm) are the most prominent, but there are a few others. Many derivative distros use one of these two package management systems. To understand "derivatives" a little better, consider that Zorin (and Linux Mint, and many others) is based on Ubuntu... and Ubuntu is based on Debian. This means that there is a lot of common features, and common software, that they all can share. And if troubleshooting a problem for Zorin, you might find your solution from someone using Ubuntu or Debian.
The main difference you will see and notice is what Desktop Environment (DE) that each distribution uses. And some distributions offer many DE's. The number of DE's is much shorter than the number of distros, but there may be up around a couple of dozen. Some DE's are "traditional"... looking similar to Windows, and some are more "modern"... looking, uh, different... like Gnome 3 (the standard used by Ubuntu, although Ubuntu offers many other choices). The graphical desktop is the look and feel that you will notice... and it's worth trying several different distro/desktop combinations to discover what suits you best. We all have our favorites, but you will have to figure out for yourself which one(s) are most comfortable for you. That's part of the fun!