My two penn'orth:-
I never bothered downloading Slayer's, it was too big to pull via dial-up and I couldn't access it through the 155Mbit connection in work. So I pulled the basic EvoX Install CD 1.2 from #xboxemu (as Freeserve users were being automatically banned from #xbins at the time). That was about 15 months ago.
It did the job nicely, a simple install with a few apps. But I was interested in seeing how it worked, how to add more apps, etc. So I started playing with it.
Within weeks, I went from knowing absolutely jack shit about EvolutionX to having my own custom install disc, which has evolved as new applications have been released. The menu is not too different from the original, but the disc now features the latest EvolutionX (with customised boot logo), 200 skins (with the saucy ones installed separately), a PC Engine emulator with 237 games, 26 homebrew games and the latest versions of 4 applications (DVD-X2, Enigmah Videomode Selector, Px HDD Loader and Xbox Media Player). In addition, a pile of "professional" applications (BoxPlorer, ConfigMagic, DVD2XBOX etc. - the sort of apps you can delete things with) are installed in a \proapps folder on the Xbox, hidden away until you enable them via FTP. This means that nobody can screw up their Xbox unless they've fiddled with it via FTP first. Only the safe applications are available by default.
Add to this the capability of formatting F: only (to get that extra space on 10GB drives), G: only, C: only (to recover a screwed dash) or the whole drive (to install a new one for example), the option of installing the applications to E: or F:, plus the ability to run ConfigMagic or boXplorer direct from the install disc (for the odd bit of tweaking) and the result is a comprehensive, custom install disc that is even easier to use than the original. For example, in the "Ultra-fast Install Menu" that's listed at the top of the main menu, a complete install can by done by choosing "Format F: only", "Install the lot to E:, F:", "Install 'too much' skins", "Fix read-only attributes". For a youngster with an 8GB-equipped Xbox, it's even easier, "Install the lot to E:", "Fix read-only attributes" does the job.
I was given a copy of Slayers 2.5 a few months ago. I checked it out (because I wanted to see if the read-only attribute fixer, attrib.xbe had been updated), found the installation and user menus to be a total headful, and gave it back.
ANYONE can make their own auto-installer. Just download the original EvoX Install CD and play about with it. That's what I did, and hundreds of people in South Wales are happy with it.