I opt out of all body scanners, including MMW+ATR.

First of all, I am not entirely convinced that MMW is as safe as they make it out to be. It is certainly safer than backscatter, but that's not saying much. It is very easy to prove that something is dangerous, but very difficult to prove that something is safe. Remember that while millimeter wave technology has been used in other applications, this particular implementation of the technology is new. If there are any health effects on a small percentage of users, they will not become clear until millions of people have been scanned and several years have elapsed. It is not at all uncommon for the FDA to recall a drug or a machine that has been widely accepted as safe for several years because some new risk was discovered.

Then there is the opportunity to send a message to the TSA and other passengers. I can't tell you how many times people have asked me why I am opting out (I sometimes say it loudly on purpose), and this is a good opportunity to discuss the issues.

I personally don't like the pat downs, but I am used to them. I have to go through them when backscatter is in use anyway, so doing it a few more times doesn't make much difference.