Some questions

Hi,

Thanks for contacting us here about this extension.

Where can i see and test a demo of frontend submission and if possible backend ?

I'm sorry we don't have any trial/limited version as our plugin are open source.
But, if you encounter any trouble of compatibility, the developer in charge can fix that for you or we can refund you.
You can see our online demo here: https://www.demo-joomunited.com/my-testimonials/my-testimonials-features.

Is it possible when a user submit to have an email to admin and after publish or not the item ?

Yes, webmaster will receive an email notification when a new entry is sent from frontend, and you can set the entry is published automatically or not.
For more information: https://www.joomunited.com/documentation/my-testimonials-documentation#toc-2-2-get-and-edit-testimonial-from-frontend

Is it possible to modify the layout of the frontend ?

Yes, you can.

Hope it helps!
Regards,

Hello,
OK thanks.

Regards,