Hacker's Keyboard is a good choice for Android phones.
I've used it, it's not a very good experience for conversation... I mostly use gboard, because of gesture input. I'm in several conversations and/or emails a day, I only have to input a numeric pin like described maybe once a month. Doesn't mean it shouldn't be improved on.
Same for iOS, fyi.
Ah true, I forget on my iPad I installed an alternative keyboard. I said Android cause I have more experience using Android. I sort of stopped using my iPad once I bought a Surface Book 2. Since it has a Netflix / Hulu app I dont need my iPad as much anymore.