How many people have tried using Siri? Until it's actually in our hands and put to the test in real world situations, it's hard for anyone to make any claims about how well it works.
It could be reliable, useful and effective; it could be sometimes useful given the right environments and inputs; it could be a complete flop. No one outside of Apple knows right now.
This is different though. Plenty of people have used Siri. The new version adds a few Apple app based intents, but we have been able to use what was essentially a beta of Siri for years. And the parent comment is right. In its current state, this is Facetime 2. Good demo, fun to play with, but ultimately inconsequential for the majority of people.
But when Siri was in app form, much (perhaps most) of the benefit that it has now wasn't possible.
Not only could app-Siri not do some of the things that people will most often do with iOS-Siri ("wake me up at 7 o'clock", "remind me to call my girlfriend when I get home", "note that I need to buy lettuce"), but you had to unlock your phone and navigate to the app icon before you could even do those things that you could do with it. If you're already using a touch/visual interface to do things, it's cognitively easier to just stick with touches to finish the job. If the interface is entirely spoken/audible, there are a whole other set of things that start to make sense to use voice for.
It could be reliable, useful and effective; it could be sometimes useful given the right environments and inputs; it could be a complete flop. No one outside of Apple knows right now.