When advertising directly through Facebook there is also no additional fee outside of what you pay for your ads. On Facebook, you are only charged based on ad impressions, whereas apps or agencies include additional fees. 

Cons 

Many small business owners starting out with auto-pilot apps may feel nervous about switching over to managing their own retargeting campaigns. A lot of this fear comes from intimidation of Ads Manager.

Ads Manager is a more complicated tool than an app, but with the many guides and free courses available to entrepreneurs looking to learn, it has become easier for beginners to manage and scale their own campaigns.