Surely - the Rapier is a laser designated device and might have questionable capability against a GA threat in IMC.
A chat with Diane Misiak of Raytheon about having a few of these HEMTT A3's heavily disguised as ice cream vendor vehicles- patrolling the streets of London to give effective cover. It will give added credibility to an arms and security conference masquerading as a sporting event.
To quote the sales blurb about the mounted weapon:
"Phalanx uses a 20 mm M61A1 Gatling gun that fires M-940 self-destruct rounds at a rate of 4,500 shots per minute. The system features an advanced search and track radar with closed-loop spotting technology that enables autonomous target detection and engagement. Phalanx can be interfaced with other sensors and systems to provide overarching protection of high-value sites on the ground"