Whenever this issue comes up, there's always a good banter of legal, required, tested, etc. Many good points are raised and made by most.
My personal thoughts are that additional braking is a good idea, and having a break-away system makes sense. But that's just me.
So...when it was time to equip our Odyssey to flat-tow behind our gasser Class A, I did my own research and here is what I found. For the model year of our motorhome, both Ford and Workhorse said in their owner's manual that auxiliary braking systems were REQUIRED on anything being towed over 1,500 lbs. Our Odyssey is about 4,450 lbs. So we were way past THAT.
At that point, it didn't matter to me what any individual State requirement was, the manufacturer of the chassis of my motorhome said that auxiliary brakes were needed. So I installed them. And yes, I can tell a difference in stopping whether the brake controller is on or off.
While I'm not one to be easily "spooked" by "what ifs" and "going to court", etc., I did figure it would be pretty easy for even a dysfunctional lawyer to find the same statement I did in the manual.
So, my answer is, check the owner's manual for your chassis and/or motorhome and see what the manufacturer says.
But in my personal opinion and thoughts, auxiliary braking systems are just a good idea. Period.
Stay safe!
~Rick