I think it hugely depends on which of the cultures you grew up in. I grew up in an interrupting culture family - interrupting was just the norm, nobody considered it rude. My wife grew up in a wait culture family. If I interrupt her she can get really mad. Over the years I've had to learn to use the wait-method when talking to her and it's made me more mindful of the two different cultures. I try to do more waiting than interrupting anymore since I now realize there's a large percentage of the population that considers interrupting to be rude.
There's also another thing that the waiters can consider an interruption, but I guess I never considered an interruption - saying something in agreement with the speaker as sort of an affirmation of what they're saying. My wife considers that an interruption, I consider it just participating in the conversation.
Instead I change my wording on the fly - I'm not actually sure he knows he is subvocalising and I've never had any indication he knows I am toying with his quirk (good naturedly - I like the guy).
I find that most gains from this style are unwound when you discover 10 minutes later that there was a critically missed assumption and you have to redo parts of the conversation. (Or worse you never realize and then build a whole project with different ideas in mind)
I definitely fall into the interrupter camp. With some of my friends in particular, conversation seems to form one long sentence being picked up by different people as it meanders along. It feels less like a dialogue and more like a melding of minds. Occasionally I'll meet someone though who I really struggle to communicate with. I find myself either frustrating them by interrupting, or I end up feeling like I'm getting lost with all of the clarifying questions and comments I'm trying to keep queued up in my head for whenever they finish.
I guess it's just one of those things where you need to get to know the person you're speaking with before leaning too far one way or the other. And of course it's challenging since the safe default to start with is the one that does not come naturally to me.
What I've noticed is that my habit of interruption is received wildly differently by different kinds of people. It drives some people absolutely crazy, and in these settings I've learned to be a little more mindful and try to restrain myself from interjecting so frequently. However, for other people, it works wonderfully and we'll get into a really fast-moving conversation where less redundant information is shared.
My theory is that two well-intentioned interrupters can have a pleasant conversation, and two well-intentioned waiters can have a pleasant conversation, but any pairing of an interrupter and a waiter will be disastrous unless both are very mindful of how they participate in the conversation.