I wonder why are there so many services that work with this kind of business model. while I would be willing to pay for code I can own, I would never invest in something in something where I can't predict it's future.
This is nice, but it does not put a valid img tag in the document source without javascript execution. That might be fine for things that don't face the public internet, but if you do any type of public publishing, you should care about having markup that describes your content independent of scripts or css.<p>This is why standard markup-based responsive images (picture and srcset) are such a big deal.
What would the advantage of this be versus using the picture tag with your own image sources hosted on a CDN? (Let's assume picture tag is widely supported for now)