The X-jet is basically a chemical injector, but it can inject the chem much quicker (up to a 50:50 ratio) and can also effectively double the "water weight" your machine produces.
For example,.. If I have a chem that should be diluted 20:1 I'll pre-dilute it 10:1 and then use the x-jet full bore to do the spraying. Now my 15 litre per minute machine is spraying 30 litres per min and the job is done much faster. As with all chem injectors it only works with low pressure tips,.. but you can still spray 30' -35' high on a calm day once your washer has a decent flow rate & you use the right tip.