The pix 506e that I got for £20 is fine. I looked at it today. I powered it up, and it worked, so I connected to the serial port, got into the monitor, downloaded the password utility, set new passwords, removed the old configuration, and put on the configuration that I have on my existing pix.
So now, if my working pix dies, I have a fallback, and that's important, because everything goes via the pix!
Then I put it away in a box, because I'm not expecting to actually have to use it.