Here's the real deal, and my personal opinion.
A conventional seal pack will seal the pump very well, but any lack of maintenance, and you will find yourself sunk! (literally) You need to get a couple pumps of grease in it after every ride. This will push out any water that may have gotten into it. If you wait... the bearing could rust to the driveshaft. When that happens, you will have a catastrophic failure, with damage to the hull, seal, and driveshaft. (minimum) AND... since the seal rips from the hull... you have a 2" hole in the hull... and you will sink quickly. The ONLY positive side to a seal pack is that you can run it on the hose for as long as you like.
The carbon seal works VERY well... and it's dam near impossible to have a catastrophic failure. The normal way it shows that it's not happy, is that you will start to get cavitation. On a very rare occasion... the seal will crack, and allow water to come in... but not a rate that will "Sink" your ski. Also... a crack in the seal is normally from being overheated... and that's from running it out of the water. (That's big no-no) In that case... it's user error.
As a final word...........
I hear guys bitch'in about 2 things with seadoo. the carbon seal... and the wear ring. Both of these items are a good thing to have, and make it cheap to do a rebuild on their parts. Also... normally I hear the complaints from people with +15 year old ski's. DO you really think that the conventional seal would last that long??? NO WAY. The "Old" style seal pack, realistically, will last about 4 years before it needs rebuilt. And guess what... it takes a press, sealing chem's, and more $$$ to rebuild.
As far as the wear ring... it's a $40 part... and fixes the pump quick. If I need a "Wear ring" for my Islandia... it's $450 because all I can do is replace the intermediate housing in the pump. (Kawi, and Yamaha are the same way)