I just installed one a couple of months ago. Everything was plug and play plus a few wire taps. It wasn't that bad... just takes a little time and patience. Lot of sharp edges under the dash though. My hands looked like a bobcat had been scratching on them by the time I was done. Next time I'll wear some thin gloves!
I have a ton of pictures and some tips.... will try to do a write-up in the near future. Here are a couple of basic tips off the top of my head.
Read through the instructions once before starting. Then, when you start, route all of the harnesses as the directions state, but do not connect or plug them in and do not tie-wrap, tape, or secure them into position yet. Just get them loosely routed. The more you start routing them, you'll find you need to move, adjust, or re-route them. Once you have everything into position and are happy with the routing (no interference issues, ect), then start at the beginning of the instructions again and start plugging, connecting, tapping, and securing the harnesses. It just works better this way and will save a little aggravation.
I didn't like the idea of the rather larger antenna visible on the front windshield. So I found a place to secure it under the dash. I think the system was supposed to have 800 ft of range. I only needed 150 feet. I tested it in an empty parking lot and was able to get around 400 feet of range from the front of the vehicle and a little less approaching from the rear. It would probably be a little less in both directions in a congested parking lot. But, It works perfectly for our short-range needs.