I'd say I've fought the flan princess or whatever it's called over 200 times and still haven't received the pink tail or rainbow pudding. The first time I used 70 sirens, then I just used 10 and kept reloading if I didn't get the items.
I think I missed some uncovering of the maps so I do not have the Treasure Hunter augment. I have all my characters at level 99 and am on my first playthrough, but want to try and get these rare items before I clear it.
It just seems to be taking so long. And add to this the fact that some members say they got the items on the first go!!!
I was lucky, somewhat. I got one pink tail using 11 sirens and without treasure hunter. I tried to get a second one, equipped treasure hunter, used up 99 sirens, said screw it, and beat the game. So you can do it, but if you're at lvl 99 the boss is a joke anyway. It's up to you if you want to waste more time or not. --- currently playing: Final Fantasy VII International, Final Fantasy Tactics PSP
FYI while I was trying to get a Pink Tail I ended up with 8 Rainbow Puddings. Took a few days of concentrated play. --- "Why do you think Ursula's so plump? She's obviously carrying Sora's seed." - Shadow Exodus