Weirdly, just a couple of hours ago I was trying to find this as an alternative "recommendation" for a buddy whom is digging around in this space. Couldnt remember the name of it, except that I had used it a while back for some simple lottie related work (and a couple of other simple tasks)... After trying various iterations of search terms that included the word "lottie" (and spending much longer searching than what I expected to) I eventually clicked through some link and landed on the Synfig site. And now, coincidently, this post shows up :)
Nonetheless... I have no idea of how this really compares to other tools, but when I have had a need, Synfig was a breeze to use for what I needed it for. Importantly, it was quick to get started with, and without needing to spend hours in tutorials trying to figure out how to do things.
So happy user and all that :)
I recently used Synfig for some simple animations and had an overall good experience. Inkscape natively supports saving to the Synfig format, making it easy to import and animate my vector art. Synfig saves animations in an XML file format, which simplifies tracking changes in version control. If you're interested in trying Synfig, there is an official tutorial series on YouTube [1].
