Most states either have law requiring one or have laws that require a certain stopping distance. And probably there are some that don't have either. And probably most require some sort of breakaway system.
In any case, as mentioned above, your stopping distance under an emergency situation will be shorter with a toad supplemental braking system installed than the coach would without or even by itself.
Yes, they can be pricey, but what price do you put on your safety and those with you or the ones you run into?
There is almost a "daily" post on this subject. Just put in "toad braking" in the search area and you'll find many post that probably will provide you with the answer you are looking for.
Personally, I will not pull my toad without one. See my signature for what I use.
Ron