I think you have really to try hg or git, to get a feel what is different.

Personally I used rcs for one year and than personally and in company cvs for another 13 years until beginning 2006. Than all projects where switched to hg  because if several developers are involved especially over the internet it is more easy and efficient. I think that mozilla for firefox and other projects also switched to hg and other small or big projects to git or hg does show that they have some advantages. To try something out and keep this changes in your personal repo and maybe reuse it at a later time can be quite interesting. You just have your personal repo for testing, commiting etc. but not push it to main repo maybe at this time. It is much more flexible.

Just convert the cvs repo to hg/mercurial and use it for several weeks in parallel. Or maybe just go to the directory where your source is and enter:

hg init
hg addremove
hg commit

than you have the current source code in hg and try it for some weeks.

Another point is if you want try something and you have a central repo of hg you can just create a directory and enter

hg init
hg pull (with https://path to repo)
hg update
to get a working copy of the source and the repo. If your new changes don't work you can just delete the directory. For big tests this is quite nice. You just commit to your local repo. If you see that your ideas work you can just push them to central repo.

Maybe if you are used to use cvs this sounds complicated but first there is also a graphical version you don't need to use command line and second after a small amount of time you see that you are much more flexible and creative with such an approach like hg or git. I use hg because in the past it was more straight forward to use and the windows version was in par. Maybe this changed over the years so in general there is no big difference if you  use git or hg but cvs is really another world. It is not so much different to use but because of the centralized nature much less convenient.

It does not matter if you use it for a small or a big project. I really recommend just to try. Just spent 2 or 3 ours with hg and you will learn a lot and it is also quite interesting. So just give it a try.