Here's "a better way" to create a "universal" El Capitan USB flash drive.
First, you need an external hard drive.
Can be any capacity, new or old, USB, Firewire, doesn't make a difference. I used an ancient firewire drive with a 40-pin IDE drive inside.
Connect the drive to a good Mac and re-initialize it with Disk Utility.
Now, launch the El Capitan installer and "aim it" at the drive.
Let the installer put a fresh copy of the OS onto the drive.
When done, reboot to the external.
Let the OS "introduce itself", but carefully create a "dummy account" -- just a username and password and NOTHING ELSE. Politely decline any kind of registration, etc.
All you want is to be able to get to the finder.
Now, put Monolingual onto the drive, and "strip out" all unnecessary languages. This will eliminate almost a gigabyte of wasted space.
Next, put CarbonCopyCloner onto the drive. Now you have a tool so that the new install can "replicate itself" to OTHER drives.
This hard drive becomes your "master".
Protect it from alterations.
Next, take a 16gb flash drive.
Initialize it.
Now, use CCC to clone the contents of the hard drive to the flash drive.
Set up CCC so that it clones the recovery partition, as well.
When done, you have a USB flash drive that can "boot itself to the finder", and clone itself to any computer that can boot El Capitan, recovery partition and all.
No, it's not "100% virgin", in that it's not a copy of El Capitan that has "never been booted".
But except for the "temp account" that gets you to the finder, nothing else has been "touched" or "set up" on it.
Just put it on the target computer, then use Migration Assistant to "bring over" pre-existing accounts, apps, and data from and old drive or computer.
And no -- ABSOLUTELY NONE -- glitches or hangs when trying to run the "official" Apple installer any more!