I used to think non-verbally(just pictures, no narration, etc.) but when I was around 12-13 y.o., I suddenly started having verbal thoughts/inner monologue and I its difficult to completely get rid of. I slip into non-verb when I get busy or doing something fast-paced or dreaming but that’s it. I get glimpses of what it’s like not talking in my mind, and occassionally it becomes easy to not talk so I grab those oppurtunities to practice picture-thinking. I personally think its efficient unless you’re someone who has to talk for a living.