I have been using rail passes for 10 years and really like them.
Its just the savings. We did a 3 month trip to EU and spent about $950 each pass, but used about $2500 worth of train tickets. So there can be a huge financial benefit if you travel frequently. You can go city to city in short hops, but we also get a base in one city near the train station, then do day trips for 3-5 days without changing hotel.
A huge advantage of the pass though is the flexibility. We have gotten to the station early intending to take a 1 pm train, and discovered another training was leaving in 2 minutes to the destination and just jumped on board, and dialed it in on the app on the train.
The app is a little problematic in a few ways. If you need to wipe your phone or replace it - as I did, your pass is gone and you have to contact them to manually restore it. If your battery runs out after a long day, you will have some 'spraining to do, to the conductor who wants to see your pass. Indeed, I was hauled into a Swiss train office by an irate conductor because I had no internet service and could not pull-up the pass for the 25% discount - so for 2 EU savings, it wasted an hour of my time.
Also its totally unforgiving about city names. (Some cities start with Saint, St, St., etc with or without spaces). Try finding the stop for Rheinfall in Switzerland - its pretty hard. Some names are posted in English and some in the native language. Its not like Google with Machine learning so if you mistype one character it still can find it - no its all confused.
Many times, there are not trains to certain places or the train takes twice as long as a bus or car. An example if Avignon to Aix-en-Provence which is 30-45 minute drive but a 2 hour train trip (either you go all the way to Marseille and back up, or you take the bullet train 20 minutes then with the buses and the rest it takes 2 hours too).
You still have to go the station to reserve many train trips on high speed trains. I have gotten errors several times when I tried to do a reservation online.