It's a rectangular device with numbers on it with which I obtain complete strut assemblies, preferably those made by the OEM manufacturer, at a cost far below the separate cost of all the worn components. I also save myself hours of time and avoid mortal danger.
Spring compressors suuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuck **** ****...
Anyway, sometimes there's no alternative. I have successfully used the $30 two-piece cheapies with the retention pins, and lived to tell the tale, but I can't recommend this.
Very interested to see what the GJ hive mind recommends. Maybe there's a better way that's not huge money.