This is still officially in Beta, according to the Shopify Guru's. That being said, we are having MANY issues that makes this almost unusable.
1.The sync with Amazon for orders once shipped used to take 10 minutes, now it takes several hours.
2. The link between products on Amazon and Shopify does not work at least 50% of the time. When you add a new product, you are supposed to link to the Amazon product. You will wait days for anything to show up, and then not everything does. Now, you need to keep inventory in sync in 2 places because when a product sells on Amazon it is not updating Shopify due to the lack of links.
3. Searching for Amazon products to see what they are linked to is terrible, and Shopify admits this. They do not have any way to search, you just have to look through PAGES of products until you may finally find the correct one. If it was never linked, you will never find it.
These are the main issues, but other exist. If they can't get this fixed, it will be an issue. Right now we are stuck every time something sells, having to go back through the list and fixing the quantity in Shopify.
Could it be good, YES! It is a long way from it at this point.