I've changed my review of this app in the hopes of saving Shopify store owners some money and aggravation. To be clear, Shopify's code has worked well for me. The problem is the crap Google slips in and charges you for. See this post for more details: https://everythingtiny.com/blogs/news/google-sells-guns-for-fun
Original 4 star review below:
A convenient app to send your products to Google Merchant. Like a garden, it takes some weeding, though. You have to check AdWords and Merchant daily. Add negative keywords for things that don't apply to your store. For instance, I sell a pewter saltine cracker sculpture which is in Google's sculpture category. Google sent me several clicks for "Zesty saltine" at $2 a click -- driving expensive unqualified traffic to me for the wrong category and description. "Zesty saltine" was added to my negative keywords the next day. Be forewarned, Google will take your money faster than a casino if you don't manage your merchant center and AdWords accounts.
A feature I would like to see added to Shopify's app is the ability to exclude specific items from the merchant center feed. I have to manually delete items that I don't want to advertise so I don't get charged for ads that drive unqualified or expensive traffic to me. I sell some items that have "tool" in their description. That puts me in competition with deep pocket bidders like DeWalt, PorterCable, Lowe's, and Home Depot, which is a waste of money for me.
I would give the app 5 stars if I could exclude products from the Google Merchant feed because it would save me time and wasted ad dollars.