Why not save yourself the stress and get one from these guys.
They advertise on here and did have a 10% promo code
www.makanifins.com/products/koi-weed-freestyle-windsurfing-fin
I have been using their weed wave fins in my twin / quad at Dutchies for the last couple of seasons and they are good.
www.seabreeze.com.au/forums/Windsurfing/Review/Makani-Twin-Weed-Wave-fins-2/
Not as good as a good regular fin but not far off and they don't give you that weed frustration! I had forgotten how much of a pain weed can be until swapping boards with Rider the other day.

I did that once, when I was sailing in really shallow waters. I made an 18 fin. The thing is, it is going to be really stiff because of the thickness and a bit more proned to spin-out. At the time I was using a Mfc freestyleweed in deeper water, and you could really feel the difference in flex. That being said, I don't know which i prefered.

I've just received (what i thought was) a new Koi 15cm freestyle weed fin from the Makani website, but it is different to the one illustrated on their site. I'm hoping they haven't just sent me an old model of the fin for my $200. So I'm yet to be able to tell you how it is, just in case they have to replace it.

Has anyone else received one like the one I've received?

This is on their site
?v=1387570945

mine

The naia is a sweet fin!!! More powerfull than the koi and for a 18cm you can easily have a 5.8 and have a blast!! for spock, grubby and not new move state of the art i prefer the naia weed!!