Keeping in mind this is a free app, I think this is a good start, but it's not working particularly well. I'll most likely have to uninstall it unfortunately, despite it doing what I need most of the time. The issues...
For starters, it's slow. Sometimes the pre-order indicator loads a few seconds after the rest of the page, sometimes it doesn't load at all. Either way the shopping experience is a little weird with this app installed since it rewrites elements of the page on load. So you'll visually see your "Add to Cart" button turn into a "Pre-Order Now" button. I don't care for that, but I could probably live with it. What I can't live with is the seemingly random denotation of items as "pre-orders" that are not pre-orders. I believe the designated tag for a created "set" is what it's using to determine that an item is a pre-order. But I have items that have no such tag that end up showing a "Pre-order Now" button or while in the cart show the pre-order notice underneath. And that's not a good thing to have showing for items that are actually readily available. This could very well be costing us sales. It's possible that having multiple stores under one Shopify login is creating a problem. I noticed while trying to set this up across my two shops that they seemed to be conflicting with each other and I could not have both shops open at the same time. All in all this needs some work. It's exactly what I need. If it worked properly it would be great, and I'd be willing to pay a few bucks a month for it. As it currently is...well, it's too glitchy to use for a high traffic shop IMO.