I follow several pro players in the Youtube, and some use huds, some not.
I made some experiences with huds, and I think it's really helpful, but I think it's too expensive to a recreational player like me, so I'm playing without it.
To use a HUD helps, but is not obligatory. First of all, you MUST know how to use it. If don't know about ranges, it's just a lot of graphics and numbers.
In my opinion, softwares are really important for multi table players, because it's almost impossible you can set all players styles when you're playing 4, 8 or even more games at same time.
I think you can totally play without it, but if you think about play poker to make money, it's a good investment.
Anyways, I saw a free HUD in the net, designed for LINUX. There is a version for Windows, but looks like the installation is veeery complicated, so I didn't try it. But Linux users are not afraid about that, don't you?
You can find it here: https://sourceforge.net/projects/fpdb/