Unfortunately, I've decided my initial review (below) was too optimistic, and I've revised it down to two stars. The app has been out over a month, and you still can't link all your Amazon listings because the linking page only displays 5 listings. When you link one, it will be replaced with another one, but once you get to 5 listings that you don't want to link, you can't view any more than those 5, so the app becomes useless. The support team has stated that have no idea when this will be resolved. Based on past experience, I expected better from Shopify. The app is not ready for prime time, even in beta.
I like what I see so far. The feature I'm most excited about is the ability to link listings for seller-fulfilled products on Amazon and Shopify so that you can keep your inventory in sync based on sales on both sites. I'm slowly establishing those links so that I can monitor and learn the process and avoid any surprises.
Inventory syncing is huge for me, and if that feature functions well, I'll be happy. The app lets you create new products on Shopify then send them to Amazon, but I haven't tried that because I prefer to create my listings on Amazon first since they require much more detail. Duplicating a listing on Shopify is a simple cut-and-paste process that takes less than a minute.
To keep inventory in sync, you have to switch from processing orders on Amazon Seller Central to processing them on Shopify. That's changed my workflow, but I'm getting used to it, and in some ways, I prefer it. Seller-fulfilled Amazon orders now show up in Shopify orders. I use Stamps.com to batch import all those orders, print packing slips and USPS labels, and then the tracking numbers post back to both Shopify and Amazon. The postback seems to occur faster than when I was batch importing from Amazon.
I use repricing software on Amazon, not on Shopify, and I'm not certain yet how that will work. You can set a price in the Amazon app on Shopify, and it will appear on Amazon. I'm waiting to see what happens when that price is adjusted on Amazon by the repricer. Will the Amazon app on Shopify set it back to the original price on the next sync or will it leave it alone until I make a revision on Shopify?
Overall, I think this is a great start, and given that it's still in beta, I'm excited about future updates. Most of the multi-channel solutions are too expensive for the size of my business, and I'd be paying for features I don't need. Ever since I opened the Shopify store after Amazon WebStore shut down, I've been searching for a simple solution to keep my seller-fulfilled inventory in sync between the two sites, and I think Shopify's Amazon app will be just what I need.