When you order a Roadmaster tow and base plates, you get a choice. They have three or four baseplate styles, depending on the vehicle. The EZ model is a hidden base plate that has connectors that twist lock into the mounts on the vehicle (this is the only kind I use/like). Once you disconnect the tow bar, you can remove the connectors from the vehicle and basically hide any evidence of the base plates.
As stated by another poster, some vehicles, often those with unibody construction, need the extra strength of the crossbar. On my very first purchase, 15 years ago, I bought the Roadmaster with the crossbar setup by accident. I hated having to deal with extra work of installing and removing the crossbar.
Again, on the Roadmaster units, the crossbar gives you the ability to use their safety cables with a metal ball on one end. The ball simply slides through a hole and into a slot on the crossbar, simplifying the cable connection. I believe the crossbar also allows for a place to mount a shield to protect the toad front end. The crossbar is also up in a more prominent area and easier to access then some of the hidden models.
Don & Mary
2019 Newmar Dutch Star 4018 (Freightliner)
2019 Ford Raptor