Truecaller uses 4 call extension, Hiya has 3 and RoboKiller has 2.
But why?
There's no limitation or lack of functionality from just using one, why have multiple with the additional complexity of managing multiple ones within the app. I can't think of any possible reason for this, so I'm mystified why so many call blocking/identification apps have lots of them.
Are they storing data in a database which doesn't support lazy loading / the ability to read a set of data in chunks, so instead they create multiple databases?