First I would NEVER recommend a Brake Buddy or any of the other "Box in the driver's position" systems.. These have to be INSTALLED every time you tow (I know they say "No Installation" but don't believe it).
I"d go with a Ready Brake (If you have not gotten a tow bar the Ready Brute has that option) or Blue Ox Auto Stop.. or if you have air brakes and it fits your towed (not a given) The M&G or Air force 1
Goign down the line I used USGEAR Unified brake decelarator (Bad install cost me a brake job rotors incuded on car) or Invisi Brake or ...
Well most any INSTALLED system that's not in your way when you drive.
As for legality. Multiple laws. Most states have a law that says something like
Aux brakes needed if towed trailer (Vehicle) is over xxxx pounds The weigh can be as low as 1500 or as high as 4000 and it is the state of registration that determines. (NOTE those weights are by memory and may be ...off.. also yoru state may be different)
SOme states only have laws that apply to "Trailers" and they will try to convince you "Oh you are towing a car not a trailer" But read the definition of Trailer (Any vehicle towed so that the weight of the towed vehicle does NOT REST on the towing vehicle.. Which fits a car towed 4 Down perfectly but does NOT fit a TT.. So there are additional definitions for the Trailers).
The other law is called "Reckless Endangerment" and if you rear end me and you don't have aux brakes on the "Trailer".. Well .. I'll be rich.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times