I was flying out of MSP today and had a bit of extra time before my flight to wander around the terminal. I'd come in with a bag of skis (from the Birkie) and was directed to an elite line (yes, I'm a silver elite on Delta, although the BOS-MSP round trip did not yield anything in the way of upgrades) as there were pretty long bag check lines otherwise. Yes, the elite programs have their perks, and work well as customer loyalty programs.
I checked my bag and was I was wandering back and forth in the terminal, the woman (and, note, she was not a TSA agent but a Delta employee) saw me again and helped to direct me to the appropriate line. At heavy travel times, Checkpoint 4 is for "Sky Priority" members only (Gold status or higher on Delta) but there is a silver priority line at Checkpoint 2. I said to her, "but Checkpoint 2 has the scanners, so why would I want to go there?"
Her response was interesting. First, she told me that generally they let you choose whatever line you want, and it's quite rare that they pull people in to the scanners. Then, she said that a lot of people liked the scanners, like anyone who had a metal implant. I'm not sure that's "a lot" of people, but I can see how for some people the MMW scanner might be preferable to a metal detector they are surely going to set off.
This seemed like a good time to raise the question: if these machines are so important, why are they only at some checkpoints? And were they planning to install them at the rest? Her answer was something along the lines of "no one knows if these things actually work, and we might be spending a lot of money on a technology which is really no better than the x-ray machines." She told me that the elite line was no longer at Checkpoint 1 (which used to be the holy grail: no line and no machines) but that it was very unlikely that I'd be selected for a scan/pat down. (Oh, she also said the scanners were faster than metal detectors. Uh, no.)
I was set to go through checkpoint 1 until I spied the line. A line like that is a terrorist's dream: a bunch of people all packed together. That and the fact that I don't enjoy waiting in such queues. So, I got in the elite line, the MMW on the elite side was turned off (and elites were being put through the metal detector) and popped out the other side, unscathed by any radiation or invasive TSA maneuvers.
So, MSP is still "safe" from scanners if you know where to wait, and may be for some time. From the airport employees' point of view, the advantage is not one of security as much as it is comfort for certain passengers. It seems like a costly way to accommodate passengers with metallic implants, but right now MSP has spent about a million dollars (six machines, $150k each) so that folks with plates and rods can avoid pat downs. Otherwise, they're not actually serving any security purpose.