Can I just use 3M Micropore tape instead of buying mouth tape?

You can, and many people start this way. 3M Micropore is medical-grade surgical tape that's safe for skin contact. The trade-offs: it's not shaped for the mouth (you'll need to cut it), the adhesive is designed for bandages rather than the movement of lips, and it doesn't have the breathability of purpose-built mouth tapes. In our testing, it scored 5.8/10 — perfectly functional, but less comfortable and less secure than dedicated options. If you're just testing whether mouth taping works for you, it's a fine starting point before investing in premium tape.