Well it is fast, and does some security checks. The interface to its image processor is not via cmdline to some imagemagick horrorshow, but not much better. From first reading it uses a dynamic libffi into the vips shared library, not a proper static binding. Cannot you do that with cgo? Looks very weird and fragile.
Static linking is now allowed as libvips is licensed under LGPL and imgproxy is licensed under MIT.
What’s wrong with dynamic linking BTW?
Imgproxy is such a reliable piece of technology, set and forget type of thing really. Put it in the cloud somewhere, add some CDN in front of it for caching and you're done.
Also a huge money saver when compared to Imgix/Cloudinary/etc offerings.