the largest, total buyer-wise mobile app marketing channel (largely driven by Facebook and Instagram), paid social is a great channel that uses deep data acquired on users to combine deep targeting abilities with the scale of the display.
this forms the base of mobile app marketing and can help reduce paid marketing costs and boost ROI by increasing the overall contribution margin of free downloads from the app store page. There are a growing number of ASO-specialized agencies, but many generalist mobile marketing agencies also list ASO as part of their services.