...not all techniques need to be specifically about the three characteristics to move you towards insight. These are just concepts to describe experience and those particular concepts work for some people and not for others.
I have to respectfully disagree here, and I'll explain why.
The Three Characteristics aren't "just concepts to describe experience"; they are the very nature of samsaric experience itself. If you're not paying attention to anicca, anatta and dukkha as the very qualities of samsara then you're not practicing vipassana.
Sure, not all techniques place the same importance on the Three Characteristics as vipassana does, but it would be more helpful to those reading this if you were clearer on which techniques you're talking about, e.g. samatha, which doesn't incline the mind towards seeing these characteristics clearly.
To understand the actuality of the Four Noble Truths, one needs to understand the actuality of the Dharma Seals. This is not debatable.
Personally, I spend essentially zero time thinking about the three characteristics in practice and I seem to be progressing just fine.
If you're able to enter into Knowledge of the Arising & Passing Away, then you've most certainly paid attention to the Three Characteristics, because you've passed through 3rd ñana (Knowledge of the Three Characteristics) to get there. To suggest that they're not important or just some sort of skillful means is to miss the point entirely.
Again, this is meant as respectful disagreement based on experience, and not as an attack on anyone or their practice. I'm a huge advocate for pragmatism and doing what works for you, but if you're practicing vipassana without attention to the anicca, anatta and dukkha then you're not practicing vipassana at all.