The fins come in three sizes/styles- male, female and child. Including a shape so there's no fussing to get things just "so". Of course I went and used my own shape - which is actually to say I used my regular shape which recently I've modified a bit to be a bit softer with more curves. That's another story though :P
Anyway I still have a "skirt" version of my "new" shape but what I was trying to say up above is that I didn't use the "skirt shape" of my regular shape with this tail set. It actually looked better with a fuller lower body, which was very nice.
The AO included with the fin set is also quite appropriate and accents the flexi design well. The overall design and execution are really very well done and I am very happy with this purchase.
I will note that at times depending on your lighting, the demarcation from avatar to prim tail is very pronounced. There is also the awkwardness of trying to use various mer poses or non flexi mer animations- they simply don't work with a fexi tail. A surprising number worked well with this fin set to my pleasant surprise, but quite a few didn't. There is also some of the normal issues associated with invisiprims used to hide part of the avatar legs- sometimes they would be very noticeable from water level or against certain textures. All of these things are common SL limitations though and nothing to do with the designs themselves.
Showa Koi Merfolk Set: Safe Waters by Goldenstar Sands
skin: Mother Goose's by milok Hermit
eyes: Shine by Brandy Rasmuson
bracelets: Legend by Fatal Raine
ears: Slink by Siddean Munro
lashes: TSM&M by Helena Stringer
hair: Waka & Yuki by yukitan Farrjones