A flyer is the advertisement the manufacturer produced to send out to distributors and machine operators. They tend to be pretty handy, since they normally have a picture of the machine and often descriptions of features. As such, they are great references when you want to know about a particular machine.
See the FAQ for more info.
The hi-res (300dpi) images are now accessible for free download. If you are a wholesale snagger of files, it'll be easier to use the "directory listing" links from the main game listings pages.
Try and pace yourselves when in hoovering mode...the content isn't going anywhere, so you can take your time.