Yesterday iPhone Dev Team released the latest jailbreak for the latest iOS 4.2.1 released by Apple. iOS 4.2.1 was released just a day before. So now when the redsn0w 0.9.6b4 is out, you can jailbreak your device on iOS 4.2.1 with it. Let me explain why to use redsn0w 0.9.6b4 to jailbreak iOS 4.2.1 and why to wait for sometime and not use redsn0w 0.9.6b4.
About redsn0w 0.9.6b4
redsn0w 0.9.6b4 is a jailbreak which will jailbreak any of your iDevice including iPhone 3GS and iPhone 4 on iOS 4.2.1.
Why use redsn0w 0.9.6b4?
I would recommend you use redsn0w 0.9.6b4 if you "badly need" to jailbreak your device. After jailbreaking you are able to install third-party apps, tweaks, themes and a lot more things. So if you need a jailbreak, use redsn0w 0.9.6b4 and jailbreak your device. redsn0w 0.9.6b4 is available for MAC and Windows both. It's safe at all and is not an 'amateur' kind of work which you can't trust.
The first reason is that redsn0w 0.9.6b4 is a "tethered" jailbreak. Tethered means you need to connect your device to your computer each time your device is rebooted. So in case your device runs out of battery and switched off, or you need to reboot it in any case, you need to connect it to your computed via USB cable and only then it can successfully be booted. Otherwise, it will stuck at the apple boot logo.
But, being tethered does NOT make it bad.
Other reason for not using redsn0w 0.9.6b4 is that not all apps and tweaks are yet developed for iOS 4.2.1. The app devs are working for it already but it may take some time. You can wait untill all these useful apps are successfully updates to run on iOS 4.2.1 without usual crashes and other problems. Even once the app updates are released, they may not be final and working. Frequent crashes 'may' occur. Or you may see some other glitches.
So use redsn0w 0.9.6b4 or not?
In simple words, use it only if you need a jailbreak badly. But I don;t see any reason that you need a jailbreak badly. You should wait to get the jailbreak to be untethered. So you don't need to connect your device each time you reboot it. comex and other jailbreak devs are already working on making untethered jailbreak. So waiting for it will be worth.
But at the end, I would leave it upto you to jailbreak iOS 4.2.1 with redsn0w 0.9.6b4 or not. It's your choice afterall.
A piece of advice : Don't forget to save SHSH for iOS 4.1 using TinyUmbrella no matter on which device and no matter if you are jailbroken or not. You'll never know when you will need to downgrade again to iOS 4.1 after upgrading.
See the post here to learn how to backup SHSH using TinyUmbrella - Backing Up SHSH With TinyUmbrella 4.1.12
The version on TinyUmbrella may be different as updated but the method is same. So save SHSH for iOS 4.1 while you can. It doesn't cost you a penny nor time more than five minutes. It's an advice for your good not anyone else.
