At First the app was not doing what I needed, after getting a hold of customer support I was able to walk though the steps needed to make the app work well. The app has a lot of moving parts for it all work well.

There were some issues getting the right support in the beginning, but after a while everything was fixed - and thank you for that.

I used Codisto to help me bulk list my inventory from popoloco.com to ebay and amazon. This tool is EXTREMELY powerful so, before using it, be sure to go through all the documentation and tutorials. The codisto listing tool enhances your store listings and it has been my experience that I have received a sales boost because of the comprehensive listing tools codisto has. This tool is more comprehensive than the Shopify channel listing tools for amazon and ebay. Codisto populates more fields than the shopify channel tools do and therefore make your listings a better performer on those channels. Recommended for patient shop owners who are willing to review all documentation. The support is very helpful but this tool works best in the hands of a responsible shop owner!

Newest Final review update; 8:32 am CST 12-27-2019 This review is in regards to a work-around for use with Amazon Handmade. There are a growing number of indications that there is a good work-around for Handmade inventory and price sync when the product is loaded manually on Handmade. A guide is promised and I will probably be back to re-install once the guide is published. Straight product to product seems to work fine for syncing inventory and price; variant work remains in progress. I am leaving the app with solid 4 stars. Good work Codisto. And Thank you.
Final review: 7:27 am CST 12-15-19 This app was installed so I could see for myself about an off-label use with Amazon Handmade to sync inventory with Shopify; answers from Codisto about this had been inconsistent so I decided to check it out myself.

Overall app review is 3 stars, but I will be happy try this app again in future.
I did not test the app with regular Amazon. If this is your situation, I recommend trying the app!
Support gets 5 stars as they are knowledgeable, have responded and tried to help me.
Ebay part gets 5 stars; it seems to work pretty well and I did not loose any data when I tested an inventory sync with Shopify.
Amazon Handmade off-label work around gets 1 star. Not yet ready for prime time. The inventory sync seems to work but at an unacceptable cost; there is a good bit more chatter going back and forth between Shopify and Handmade than I understood. The chatter produces with some serious results like erasing product descriptions, changing production times, removing category assignments and removing listings from the Amazon catalog entirely. And once you have synced your Amazon Handmade, whatever you do, DO NOT disable the offer as it produces some of the above consequences, I was told.
I will be following Codisto in their facebook group to watch for updates and will hopefully try this app in future when work around bugs are worked out or a definitive connection is made with Handmade. And maybe even the addition of Etsy.

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Update: 8:07 am CST 12-11-2019 5 stars for support with Noel. App is set up and seems to be working as advertised with a workaround for Amazon Handmade. The Amazon Handmade products (loaded manually on Amazon Handmade) have synced quantity with Shopify. The issue with Amazon Handmade seems to be the UPC which is not required on handmade goods. I will continue to update this review as the functions are tested. I really appreciate support working to help over the phone. This company clearly is interested in becoming a success.

Update: 7:09 pm CST 12-8-2019 Thanks to Noel, on the other side of the world, for helping with set up; 5 stars to Noel! There was a timing issue during set up which was explained well. And Noel was able to talk me through part of set up with Amazon which was most helpful. Codisto support is working with me at my own pace, since this app is way over my head. Situation is looking favorable for inventory sync with Amazon Handmade. And being able to talk on the phone with Noel is GREATLY appreciated. Now let's see how the app runs and works.
This will be a running review, updates at the top of the thread. App is installed, but not yet set up. 3 stars. Not for beginners. Information from support is conflicting at times, so am trying the app out to see for myself. My need is to be able to post all my handmade items for sale on all my channels and have the inventories synced back through Shopify so I don't oversell. Amazon Handmade is an Amazon outlier with respect to most apps. I have received info from one support person who says that if products are listed manually on Amazon Handmade, they will sync back to Shopify to keep inventory straight. This remains to be seen.
This morning I processed a return/refund on Amazon Handmade and then got a new identical paid order showing up on my Shopify hub coming from Codisto; pretty sure this is a glitch, as I cannot confirm the purchase on Amazon. Inquiry sent to support who has been responsive so far, though probably in a different time zone.

I used the app to list my products on eBay. The installation steps are quite easy. I enjoyed the ease of it recognising my inventory details and easily importing it into the app. I equally like the ease of setting the shipment for my products. I set the category for my product to be set automatically on eBay. However, I do not the category my products are automatically listed on is appropriate for my product.

Easy to use. Good for individual items on Amazon. For variants unsuitable, because texts are not customizable. Unsuitable for Ebay because legal texts are not safe.

easy to use once you get used to the "excel style" layout. for the most part the app syncs and lists things superbly and would recommend.

for the price, the pros outweigh the couple annoying cons that we've experienced thus far.

Pretty good app.

Pros: When your FBM order fulfills in Shopify, it notifies Amazon and fulfills on Amazon on autopilot.

Cons: You have to manually "send" the order from Codisto to Shopify for your FBM orders. (you can choose to auto send everything, but then all your FBA orders would flood your store).

Links eBay sales to Shopify as wanted, and the app support was prompt and helpful when needed. Would recommend. Backend could be more simple to use, with so many credentials needed to add to products

They are trying to improve all the time the level of communication.
In near future I am sure I can make my review 5 stars!