We have a Tekonsha P3 in our Discovery 4 which is pretty new, and so far have only towed a camper trailer with it, but absolutely no problems so far. If you follow the set up instructions you can't go too far wrong. Once you've initialised it and set up your brake type and boost etc according to your trailer/car weights etc, that's pretty much it, and it does the rest. The instructions that come with it and the diagrams are easy enough for me to follow, which is saying something.
We certainly didn't need to baby it while towing, just let it do the job. We went for this brand because it was highly rated amongst Land Rover owners and is fairly easy to operate and read (need your glasses though!). It lies just above the driver's left knee. Doesn't get in the way whilst driving, but it's nicely to hand. Installation was by Ritters in Melbourne. Oh, and you can copy the instructions on to your phone or laptop via pdf and just carry them round in case you need them.