Bellflower can be kind of wonky if you have enough Charisma, particularly if you're working on a build that can make good use of high Charisma (Nereid Battledancer/Paladin or such).
With 30 Charisma, one use of Bellflower to boost Charisma will give you +10 for a total of 40, then use it again to get 45 if you like and again to get 47 and even 48 if you have time and uses. At any point, you can apply the +10 - +18 bonus to other ability scores too. These don't stack with the typical enhancement bonus items, though, so you won't see 30 natural Charisma for a while without a race that raises Charisma. Even so, that just means it rises slightly more slowly (for instance, 22 Charisma leads to 28, 31, 32).