Tracking phones in shopping centres — how do you feel?

I was in a shopping centre in Reading today, and this notice caught my eye:

Despite the protestation that "no personal data is recorded," it's quite clear that information about me — or, perhaps, my phone — are being used to provide information to the shopping centre, and perhaps used in other ways.

It was a system I had heard of before, from a company called Path Intelligence. It does not work by using data from the mobile operators, but by careful monitoring of certain frequencies used by mobile phones, to detect phones as their users move around. There was quite some controversy around Path Intelligence in 2011, with the system being labelled as "secretly tracking" and "snooping," but it seems to have gone quiet since then.

I did come across this Freedom of Information Act request, made by Eric King at Privacy International, asking the Information Commissioner to produce any materials resulting from a discussion with Path Intelligence, and the results make for quite interesting reading.

How do you feel about this? Sufficiently invasive to be in need of regulatory attention, or a trivial and inherently harmless use of information gathered from the airwaves? Would it make a difference if you could opt out (something Path Intelligence does not offer)?