Cobras are GREAT! The only people that I know that don't like them are running steep creeky stuff, where they don't want the oars to dive and jam or break on a rock. But then again, some that do run that stuff use cobras anyways.
Get the deluxe, with the thread and nut, so you don't risk bending the shaft.
I only know of one person that uses the convertibles, and they were happy. I'm leery of it breaking at a key time.
I am a river, babe - I've got plenty of time, I don't know where I'm going, I'm just following the lines..... - "We are water" by Shaye