I'm a big fan of their cross-platform attribution, especially because we send a lot of our users from our website to our mobile apps. Also, we are big fans of being able to track mobile app install campaigns from Facebook, something we couldn't do with Firebase.
Dislike is a strong word, especially when it comes to an almost complete platform. I would like like the ability to send push notifications and segment users within the dashboard. That would be extremely effective for our marketing efforts.
I recommend utilizing Branch no matter the amount of users you have. The prices are extremely reasonable, and when you are in scaling mode, you need to understand what marketing dollars produce the largest ROI; and Branch helps you do that.
They also have some great integrations with Apple Search Ads, MailGun, ActiveCampaign, organic social media and content, so you can track your users across all channels. This complete tracking is essentially to really accelerate growth, and understand your companies growth loop.
A big plus was the Web to App feature that track cross-platform for when users go from web to app.
We are solving cross-platform attribution and being able to determine what touchpoints we need to hit in order for our user to become a customer. We've realized what our most effective paid campaigns are in terms of ROI.