Sorry for getting here late, we had to get the optional shim for our 3. The dl3 was fine one trip with 3 bikes, but fell off (at 5mph, on the first corner, thankfully!) with 4. With the shim in it feels much more solidly attached to the car, but I've not tried it out yet.
thanks for the reply. I'm not sure what you mean by the optional shim?
I've ordered the DL3 with extra carrier for 4th bike, as we have two light adult mountain bikes and two kids bikes