I wrote a css override to make it more encouraging.
The code below makes the custom message you write look fancier, and removes the discouraging ! sign. I'd much rather block sites gently.
Thank you for such an awesome plugin though.

body {
background-image: url(https://source.unsplash.com/collection/139386/1920x1080/?sig=) !important;
background-repeat: no-repeat;
background-size: cover;

}
h1, table, #exception,#options, #switch,footer,header{
display:none !important;
}
#message {
width: 100%;
text-align: center;
font-size: 5em;
padding: 0 !important;
height: 100%;
display: flex;
align-items: center;
justify-content: center;
font-weight: 100;
background: #222222ba;
margin: 0 !important;
}