Well, a minor point but if you have two people who are traveling together the Eurail Flexipass is cheaper. Even so, it is only worthwhile if you use your “days” for major transitional travel that takes hours and hours and hours. For short hops between nearby cities, buying tickets is better.
The info on all the many varieties and flavors is on the STA site I posted. the trick of it is, it’s rather difficult (but possible) to figure out what train fares in Europe cost so as to make a comparison of relative value before you get there. At the time (1997) we determined that a train ticket had to cost more than $50 US before it was “worth” a Flexipass day. We got a 5-day pass for 7 weeks of travel and used them for the following legs: Madrid-Barcelona, Barcelona-Montpelier, Arles-Florence, Verona-Budapest, Prague-Frankfurt.