The advantage to a four down tow is that you have near zero tongue weight so you are not adding a load to your truck's suspension load. Of course you have the strain of getting it all rolling and then you are really looking at your ability to stop the whole affair. Trans coolers, cooling system loads etc. are factors to consider. With a properly setup independent brake controller for the towed you can be pretty darn safe. That and you can move weight from the TC to the towed. Many states have a rather liberal approach that focuses on the combined rig's stopping distance.