We have used it for detection at a difficult site - the controller is adjacent to a bridge and the road falls away on both sides making line of sight difficult. However the Janus 3 has been working for about a year with a unit on each side of the bridge and a receiver on a pole near the controller and it has proved to be reliable despite the potential problems.
We have used various versions of Janus, mainly to link remote pelicans to an OTU at an adjacent junction, so there are no safety implications if the link fails. We've found over the years that you need to bear in mind the normal caveats about anything to do with wireless - that range and reliability depend on local environmental factors which need to be taken into account. However, once set up we've found them to be pretty reliable; sufficiently so that we recommended the use of Janus to link the ramp metering controller to the traffic signal controller on the opposite side of the M1 at the J33 Integrated Traffic Management Trial. That installation has been in for about 18 months with no problems.
We have had a Janus installed for nearly three years without problem - have also recently had a second installed both across bridges that could not be ducted across.