Hum.. which android version are you on? The native selector is extremely fast here. The goal is to have and integrated solution like Twitter, but that is a lot of code.
Discussion
In my case is fast & ugly, but ig shows the latest image wich usually is some image I just download to post, so it gets the job done really well
Android 9. Takes some 30 seconds to open the image dialog. Don't know why, other apps open it quickly enough albeit crappy to choose images.
Android 9