In my experience, it's really best used for a low level party. By the time you hit 5th level and are casting fireball on your own, it's no big deal, but in the hands of a 1st level character, that 10% chance of getting fireball can be a game changer in some fights.
I game one out in a 0-level funnel (inspired by Dungeon Crawl Classics but using 5e rules) and it was a blast.
I game one out in a 0-level funnel (inspired by Dungeon Crawl Classics but using 5e rules) and it was a blast.