Package registry have a limit of 500 MB for free plans and 1GBs for pro. While this value might be more than enough for lets say node packages, for Docker images I think it´s too small.
If you have an image based on ubuntu it will already be bigger than 100mb. with a couple of releases of your app, you will reach the limit pretty fast.
Even with an alpine image with 30 MB, if you have a couple of versions and some feature branches, always building new images with CI pipeline, it won’t take long to reach that limit.