As mentioned. A properly adjusted helmet is a key factor in its effectiveness.
My wife and I are in the market for new matching helmets (We ride our tandems a lot) and the next ones will be MIPS.
Good guide here.
https://www.nhtsa.gov/sites/nhtsa.dot.gov/files/8019_fitting-a-helmet.pdf
I've only been in one crash and my helmet came through it unscathed. I hit a pothole doing 25 mph, the handlebar twisted and I was airborne and face planted into the pavement. Helmet??? Not a scratch. Me??? broken wrist, elbow, cracked ribs and a year of dealing with the injuries.