they are only to be used offroad and at low speeds. you can turn with them locked, but it is better to disengage the front while turning on trails, they are really only needed while climbing. although, i do leave my rear locked whenever i'm offroad as it eliminates the weakest link in the rubi rear axle, the lsd.
you can do the h4 upgrade on the cheap or spend a few bucks and go LED. i have no problems with the H4's, but i think i would have bought the truck lite LEDs if they were $400 when i did my h4 upgrade