Eric, did you choose the middle option : Redirect to another URL
or the bottom one : Redirect to a Custom HTML Page?

Is this something that will only work when the form is live (not in preview)?
I had it set for Redirect to another URL, but in previews I get that JS alert when I click submit rather than going to the site.

middle URL

Just wanted to let you know... I figured out the secret to getting this to work:
The URL has to be DOT com, not COMMA com!
Time for better glasses

^funny.