Come on, man. "Coming Soon" means it's going to be released later. If you want to purchase before release, I believe Brian will appreciate your early support. But if you decide to look around or want to watch the free overview video first before purchase, it's totally up to you.
I don't know how good you are, but if you say "in my case, when i really need to learn and learn fast - this is totally useless for me." makes me feel you designed the whole iOS system.
Another thing, think before talk. No matter how many years of experience you have, you're here to learn. Show some respect and appreciation to your teacher. Not only on internet, in your real life.