As a preamble I'll say that every writing "rule" should be seen more as guidance than a strict rule. Which means there will always be numerous exceptions where that specific advice doesn't apply, for whatever reason. Your examples can all work fine on a standalone basis, but I wonder if the frequent repetition of certain filter words can become too distracting. So this is also something to consider, rather than the filter word in and of itself. I would also think about whether some of these are actual filter words, or just perfectly plausible ones. In your example #4, "heard" is not a filter per se, so that shouldn't even be a question (like you implicitly assume). The use and frequence of such words can also depend on the rhythm you want your sentences to have, the genre you're writing into, the emotions you want to convey. The sentence "And then I saw him" carries a different weight than its "unfiltered" equivalent, because you'd then have to explain who it is that you saw. While maybe your intention in the first place was to let the tension rise, before telling the reader who the character saw.