Quick report from TPA on VS129 yesterday. MPC line was clearly signed, though the employee verbally directing people was only differentiating between US and non-US passport holders.
It was very fast. The officer had a problem with people having their phone out as they approached, I get it, but having an app does rather lend itself to people wanting to show they have been directed to the MPC line via the app. Appreciate it's the facial rec that proves it from the officers perspective.
All said made it smoother, though baggage reclaim was immediately behind the booths, and to be honest I think most people in the regular line were though before the baggage

. Even upper class baggage. So my summary is that it worked well, very slick but not mandatory at an airport like Tampa which is slick anyway.
Was a good test that can travel on same MPC with family who have a new ESTA (though have had them in the past) and me on an ESTA entered on previously.