DEI (Clifford & Viper) is good stuff. Did one on our VW in 95 after our CD player was pinched and the dash was hacked up to get it. Prior to that walked up to my car with the door open, windows down, motor running and no keys in the ignition. Later discovered there was a tool called a Lishi that granted access to anything.
Did a Clifford 3G with tilt sensor, remote start for a 5SP M & a window + sunroof closer. The install took 8 hours and bummed they said it’d be two. The installer did it to spec and had only one issue with it in 25+ years. Amazing company as all their 3G & 4G products are backward compatible and upgradable.
Unfortunately their products are only as good as the installer. I’ve seen guys use vampire clips on installs, then blame the product. The installer is key.