Re: [Nutaku] Flower Knight Girl
Whether or not you should do the 80 Stam SG depends on what your goal is at the moment. For instance, if you're hoping to level up today, you probably shouldn't do it. But if you're trying to level up a high level 5*+ girl, it might be worth it, because leveling those up with just 5-year Manyus costs a ton of gold.
For instance, I'm in the 70s now- farming the most efficient map (14 exp per stam) would only get me about half a level's worth of exp in exchange for my whole stam bar. I can try and prop that up with gatherings, but multiple level ups in a day aren't really feasible for me any more unless I blow Flower Gems (and I'm very Scrooge-like with my gems!!). So I find myself going for the 80 stam garden now, because I need my teams leveled up to 3-medal 12-5, which is a real bitch with low girls.
For what it's worth, the JP wiki seems to suggest that each chest from the 80 stam SG has a 15% chance of containing a level 100 manyu (a split of 35/50/15), but I don't know if that's accurate for the English release.
tl;dr: if you're below level 40 don't even think about it, if you're below 65, maybe/maybe not, if you're over 65, go for it (unless you have enough stam to level up through other means, obviously)