The number of MITM attacks that's thwarted for me remains zero, while sites forgetting to renew their certs despite setting HSTS is a fairly regular occurrence.

Not being able to access the web interface where you have to manually upload a new certificate due to HSTS and the old certificate having expired a couple hours ago...

Yeah it’s more of an annoyance for sure. I only discovered it was a thing when intentionally MITMing a domain on my router