The difference is mainly around the Charging amperage the two units are capable of. I have not had any problems with the 80, however, I have and use a winch so I wanted maximum amperage between the batteries, so I opted to upgrade to the 160, which was not available when I first ordered.
In reference to the "relatively old repackaged question, no, not at all, it's one of the slickest implementations I have seen. The competitors for the most part use solenoids, I don't think you can get much older or repackaged than that. If you were budget minded, and wanted something decent, there is another one out there, I could bring in for you for about 80 bucks which is a
halfway decent alternative.
In my opinion, go with the 160, and you will have the maximum capacity, and options and you can move it from vehicle to vehicle if you upgrade later, it will last forever. The warranty is also excellent. I believe if it ever fails, he will replace it.
There are "kits" specifically designed for Land Rovers, as well as some other vehicles, or generic kits. These are hugely popular in Australia. I recommend the complete kit, because it will come with all the wire and other stuff you need for the installation. Here is a bit of a description on the 160
http://www.traxide.com.au/isolators/usi-160---160-amp-winch.html
The 160 also has an optional switch which allows you to change it from several different modes or behaviors more conveniently. This alleviates the concerns voiced in this thread. Additionally, due to the design, you can add a solar charge controller, as I did at the rear of the vehicle and it will charge both batteries. Here is a summary of the modes on the 160.
IGNITION ON Mode
Cut-In at 13.1v, Cut-Out at 12.6v ( similar to other isolators )
SHARED Mode
Cut-In at 13.1v, Shared mode 12.7v, Cut-Out at 12.0v
See full details of the advantage of the SHARED Mode on the SC80 Isolator page.
JUMP START Mode
Manually selectable between 10.0v and 12.7v
WINCH Mode
Manually selected above 13.1 ( motor must be running ), but once selected, will operate down to 10.0v
TIME-OUT, energy saver.
The USI-160 also has a Time-Out feature, designed to avoid wasting energy if a vehicle is not used for some time.
The Time-Out counter starts when ever the voltage at the input of the USI-160 drops below 12.7v and Times Out and shuts down after 72 hours ( 3 days ) from when the voltage first dropped below 12.7v
Any time the voltage at the USI-160 rises above 12.7v, the TIME-OUT counter is reset and suspended.