If you haven't seen Marc Remmert's video on creating a WinFE ISO, here is his video. Although the WinBuilder method greatly simplifies what Marc shows in his video, it certainly recommended to see what is actually happening to a Win"P"E to make it into a Win"F"E, no matter the process used, at least understand the changes being made, the reason for the changes, and the validation of the changes. And for those that insist that WinFE is not WinFE and that it is WinPE...well, you are sorta correct. WinFE is the 'forensic' modification of a WinPE, so it really is something different.
On the WinBuilder topic, a great group of beta testers have started to put WinBuilder through its paces. Again, although the end result is that you will be able to create a WinFE ISO with a few clicks, it is best to know what is happening behind the scenes and Marc's video gives you that insight.