I would not count on it to pick up cars if you have other riders right behind you. I find it to be hit or miss in those situations.
That said, I’ve found the Varia radar to be one of those rare products that far exceeded my expectations when I bought it. It’s unbelievable how well it tracks multiple vehicles in challenging conditions. It might be the coolest gadget ever, just really impressive technology. It’s not a guarantee you won’t be hit by a car, but it’s a great way to improve situational awareness to minimize your risk.