For me, the Coosa felt very tippy. The only thing it really has going for it (in terms of stability) is the width. The hull shape is normal.
I must admit I got caught up with all the hoopla regarding stability and little design gimmicks. I bought the yak after watching Drew [guy in the coosa demo vids] walking around and jumping like it was nothing. As it turns out, if you look past it all, you see that he's actually not very tall, nor stout.
Why do you see more Cooas for sale? IMO I think it's because once the honey moon phase ends the original buyers realize that it's a VERY technique specific kayak (rivers). They then end up selling them to buy more well rounded kayaks that can tackle rivers, lakes, ponds, and salt without sacrificing as much as you would with the Coosa.
If you're looking for a river specific kayak, the Coosa has much to offer, scuppers, storage, maneuverability, very comfortable seating, and stability. If you're looking for a well rounded "do-it-all" type kayak, stay away from the Coosa.
I for one am 100% happy I jumped off the Coosa bandwagon early.