I love this app (in theory!). The main problem is that it doesn't consistently work, especially on i phone. On desktop it works most of the time. On i phone it only works occasionally, which is a big shame because obviously a lot of traffic these days is on i phone. If they could resolve this issue it would be great. I reported it to them and they said they will look into it.
This app seemed promising. However, it needs to be updated to work with Shopify's dynamic checkout feature (i.e., if the customer selects the "Buy It Now" instead of the "Add to Cart" option, the app doesn't add the coupon code at checkout).