I put a used Viper 791XV in my 4Runner years ago when I got it. I've had a couple of times where low battery has caused the alarm to act funky, but what electronics do work w/ out proper power?
I really wasn't a huge fan of the DEI products, but w/ Clifford/Avital being bought out so many years ago it doesn't leave a lot of choice. DEI owns pretty much everyone. I put another used Viper in my MR2 recently, and its been working great as well. So I'll say you can't really go wrong w/ them.
As far as installation, you get what you pay for. I did professional car audio installation for years and the price that they get paid to do an alarm is for a lot of splices, crimps, and t-taps. Scotch locks if you are really unlucky. I spend my time on my own cars and do it right, and it shows by not having problems with the units later on. Both alarms that I have were removed from "race cars" at my previous job because they did nothing but continually go off and have problems, and they were suppose to be thrown away lol.
You can check out my MR2 install
Most Designs » content … there, sorry the 4Runner install was long before I had the blog going so it didn't get many pictures or more than a quick mention in my build thread.