Originally Posted by Drip

Nope.
1. It only goes into the Bracelet slot, not into the special equipment slot.
2. It doesn't stack with abilities increasing crystal drop (which is not too uncommon, so with picking certain units, you easily get way more crystals to drop).
3. No stats.
4. You can't upgrade it (yes, it is stuck at lvl 1 forever!), so it won't get any +def or +atk that way either.
5. Even if you like to use your Solar Blast, 15% is hardly noticable. It becomes noticable once you get over about 50%, which is impossible using this bracelet, since it doesn't stack.

Hm. I wonder if the not-stacking with character ability applies to the entire squad or the character wearing it? For instance, if Hollyhock is the only crystal booster in the party (20%) it seems clear that she won't benefit from the bracelet. But what if another girl in the squad who had no boosting ability wore it; would the overall total go to 35% or would the 15% just be ignored? If it's ignored, then I don't even see the point of the bracelet.