I began using inkFrog in their very early days (possibly 2014-2015?) and I've never gone back to anything else. At first I loved the simplicity -- With one simple template creation, I could finally make changes to all of my listings, across multiple accounts, without doing it by hand. Every listing I created, and every photo I uploaded was just there in the library -- forever. This turned out to be huge. Something I haven't sold in a year has come back on the market? No need for new photos, new descriptions, I just pop into the library and publish it.
Over the years, though, they have added an incredible number of features. From syncing with other platforms like Shopify to creating shipping labels, there is a constant introduction of more powerful features.
Sometimes the simple things clinch it. I sell a lot of items where the product photos I get are 400 x 400 -- too small for eBay. I just click the photo within the new listing, change the canvas size, and I'm done. I had prior done this manually through an external photo editing program.
The customer support has been superb and personal. I also love that there are frequent webinars so that you can get training/information on the new features they launch (or just get a better understanding of the old ones).
I have tried an endless stream of eBay/eCommerce software packages, and inkFrog and ShipStation are the only two that I have stuck with since the beginning. Highly recommend!