I went with the bank boon but just cracked open a cookie.
Going to track the cookie just to see what my stats are. Obviously I can't know what I would have gotten by refreshing, but I can track how often I would have refreshed.
1) water, Baby Ruki Board Book, 2.5k NP, +3 defense
2) ***air, 2175 NP, +3 movement
and bonus quest (when I went to complete my training): dark, 490 NP, +3 HP
3) battle, 100k, +3 str, +3 def, +3 HP (a time savings, but probably pretty even compared to the codestone cost -- at least it didn't cost more than training, though! The item was only 7.5k two months ago.)
4) **grey, 540 NP --> earth, +3 def
5) light, 2.2k, +2 level
6) fire, 1.3k, +3 str
7) fire, 1850 NP, +3 str
fire, 1262 NP, +3 str
9) light, 1745 NP, +2 level
10) dark, 1 NP, +3 HP
*** definitely would have refreshed
** Might have refreshed
Stat increases:
+9 HP
+4 level
+12 str
+9 defense
+3 movement
I only got three movement, so I probably wouldn't have refreshed but one or two times. Assuming one of those refreshes was a great faerie, my net increase in stats would have saved me a bit fewer NP than I gained from the bank boon. I'm happy with my choice.