Last time I looked into Gitlab CE I decided not to go with it because there is no pull mirroring outside of their Premium offering, I would consider this a limit.
Limits are not features. There are no limits on number of users, number of repos, etc. etc. However, you're fairly obviously not getting any of the features that are in the paid tiers of gitlab's own offering. It's open core[1], rather than just open source.
You don't get SSO user-group mappings in CE, but heh, if you use Terraform that is easy enough to manage manually even at that size.