Not really mobile friendly

Definitely a problem. I just fixed it by hacking the plugin’s stylesheet.

In the plugins/storefront-sticky-add-to-cart/assets/css folder, open the style.css file.

Above the line that begins

.ssatc-sticky-add-to-cart {

Add

@media screen and (min-width: 768px) {

Down around line 72, comment out the line that reads

@media screen and (min-width: 768px) {

My final code looks like this:

@keyframes slideInDown {
  from {
    transform: translate3d(0, -100%, 0);
    visibility: visible; }
  to {
    transform: translate3d(0, 0, 0); } }
.slideInDown {
  animation-name: slideInDown; }

@keyframes slideOutUp {
  from {
    transform: translate3d(0, 0, 0); }
  to {
    visibility: hidden;
    transform: translate3d(0, -100%, 0); } }
.slideOutUp {
  animation-name: slideOutUp; }

.animated {
  animation-duration: .5s;
  animation-fill-mode: both; }

.animated.infinite {
  animation-iteration-count: infinite; }

@media screen and (min-width: 768px) {
/* put here by LDY*/

.ssatc-sticky-add-to-cart {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 999999;
  transform: translate3d(0, -100%, 0);
  padding: 1.618em;
  overflow: hidden;
  zoom: 1;
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.2); }
  .ssatc-sticky-add-to-cart img {
    max-height: 3.631em;
    width: auto;
    float: left;
    margin: 0 2em 0 0;
    padding: 3px;
    border: 1px solid rgba(0, 0, 0, 0.1); }
  .ssatc-sticky-add-to-cart .ssatc-content {
    position: relative;
    line-height: 1.387; }
  .ssatc-sticky-add-to-cart .star-rating {
    display: inline-block;
    font-size: .75em;
    margin-right: 1em;
    -webkit-transform: translateY(1px);
    -moz-transform: translateY(1px);
    -ms-transform: translateY(1px);
    -o-transform: translateY(1px);
    transform: translateY(1px); }
  .ssatc-sticky-add-to-cart .price,
  .ssatc-sticky-add-to-cart .stock {
    font-size: .857em;
    opacity: 0.5; }
  .ssatc-sticky-add-to-cart .button.variable:after {
    content: "\f106";
    font-family: "FontAwesome";
    margin-left: .53em; }
  .ssatc-sticky-add-to-cart .price {
    margin-right: 1em; }

/* @media screen and (min-width: 768px) { */

  .ssatc-sticky-add-to-cart .button {
    position: absolute;
    top: 0;
    right: 0; } }

@media screen and (max-width: 767px) { */
  .ssatc-sticky-add-to-cart {
	  display:none
  }}

Hey guys,

I just stumbled across the same problem. I logged it (https://github.com/woocommerce/storefront-sticky-add-to-cart/issues/10) and sent in a patch. Hopefully the devs accept it and make it more usable on mobile. 🙂