I get where you’re coming from, but I’m a little more cautious with filters than most folks. I used to do the “hold it up to the light” trick too, until my HVAC guy showed me how much dust and gunk can build up in spots you can’t really see. Even if it looks okay, sometimes it’s already restricting airflow, which can mess with your furnace or AC over time.
I get not wanting to waste money—nobody does—but I’d rather swap out a filter a bit early than risk a bigger repair bill down the line. Plus, if you’ve got anyone in the house with mild allergies (even if you don’t think it’s a big deal), a fresh filter can make a difference. Maybe the three-month rule is overkill for some, but I treat it like cheap insurance for my system. Just my two cents...