Hello Gera,
RW is a lot more stable than MSTS was, if for eymple a building or some scenario object is missing in a freeware route, it wouldn´t show up in the game, nothing more.
If scenario rollingstock is missing you will get an error message, and thats it,
But sometimes RW crashes too, but you can´t say if a freeware route was the problem or not.
Installing a route differs sometimes, one route comes as a rwp. (RailworksPackage) that has to be opened with the packageManager, some routes have to be installed by hand, then its as complicated as it was in MSTS

.
Most freeware routes need other assets (free- or even payware) that need to be downloaded from elsewhere and have to be installed.
But in my opinion, installing new stuff to RW is much easier and safer than it ever was in MSTS.
In the download section from railworksamerica, you can see the README files, so you can decide to try the route or not, and in this forum you will find many nice "railworkers" that will help you too.

Give it a try!