I have been working on a New Year's Resolution marketing campaign for Brooklet with the Youtuber Jem. She produced this excellent video advertising Brooklet. I also added a handful of features to the app for New Year's resolutions.
So far around 11000 people viewed the video, 525 have signed up in the app, 6 have signed up for the premium subscription.
This is great but for the price of the video ($1k), it's not worth it yet. However, I think other influencers would charge less. People are still signing up so this number could change in the coming days.