If you want to test SpeakOut!, of course, you can always install the SpeakOut! WordPress petition plugin on your own site and delete it if it isn’t suitable.
But if you don’t want to do that on a production site, here is a way to try it out on a dummy site https://tastewp.com/new/?pre-installed-plugin-slug=speakout This is a cool trick TasteWP does to create a test site instantly and install any plugin. You can play with this site for 2 days for free.