I've two questions/bits of feedback.
I've created a sign-up form and embedded it my site, but I can't find the options (if they're there) to edit the "Thank You" message in the actual sign-up form, or to add a redirect link to the button.
I also have the Constant Contact plugin on my Wordpress site which does offer this level of customization, but the form itself looks horrendous compared to the native Constant Contact form - at least without excessive CSS editing.
Am I missing something?
There are several types of lading pages that you can create in Constant Contact.
The type you are describing is a Lead Generating Landing Page. This link has the direction on how to make a Lead Generating Landing Page, including how to edit the thank you message and add the redirect link.
We completely understand how a thank you message for an embedded form would be important to edit. Unfortunately, at the moment we do not have the ability to do that. I will track your feedback on this as well as your feedback on adding more text to a landing page sign up form. Thank you!