Like stated before. Full hydro is not street legal. Hydro assist is legal. Off Unlimited is complete crap and their customer service is shit. I have been running a PSC hydro assist for about 25k now and it is f@ckin awesome. I have not had any problems with it. Turning my 37 mt's is easy at a stop. PSC will also drill and tap your steering box for you. There are other companies out there that make hydro assist but I recommend PSC.
I don't know to be honest if it is illegal. I did a little looking around for shits and pickles and the ONLY state that really says anything is Tenn. They state that you cannot alter the factory steering components and or system. All the others are concerned about the size of the steering wheel!
Other little things but that is the just of it. I looked at composite vehicle specs also. There is no cut clear policy that I seen, like say handle bar height, on motorcycles. The only thing mentioned was on some site was IF you were involved in a accident say do to a failure of that component that a attorney might have a field day and your insurance might not cover since you altered the vehicle. Makes sense
I just looked around like I said mostly on Jeep sites some where I post. Some have installed these systems for obvious reasons and have the same concerns. of street legality.