only that they wear out and get ripped off after while and dont look as cool. Upside is they do not leak at all (unlike scuppers), are cheap as, easy to install, you dont need to use pvc pipe with them like the scuppers on superjets. I will be going back to these on my SXR after loosing the whole ski at the port for a week due to leaky scupper valves.
isnt the downside when the ski is in the water upside down it will fill up with water real quick because the duckbills let the air out of the engine cavity
I would imagine scuppers would be much worse from that respect but yea thats another downside to any sort of drain
Try these as another option, everyone here swears by them. http://www.pwcdoctor.net/VERSIPLUG_MAX.html
You can them order them through SkiMD - they are the only distributor for Hot Products in NZ i think...