Has there been any reports of the maintenance requirements and costs (either preventative, or repair/replace) of any of the AIT technologies?

These units have been implemented rather recently, so their up-time will be predictably high. Yet was wondering what their reliability was, at least in regards to costs (hey, we are paying for these, after all). Are they based on currently implemented technology (eg: hospitals, industrial, etc), easily maintained and/or repaired, are they modularized for servicing back at the plant, etc?

Are there any concerns that we're going to start seeing these out-of-service for use-based maintenance, field-calibration, repair, etc? Has the TSA indicated what they're going to do with the WTMD (leave them at the airport storage) in case there's a strategic need to over-populate the lanes, etc?

The WTMDs appears to be (technologically) simple (including field calibration by the TSOs), and the reports on the puffers speak for themselves. Thoughts on the operation impact of AIT reliability and predictability?