well its just an example of something else that works , its not my idea , a chap in the states used it first and i wanted to try it .
I would now have the flow of a very big pumptec , about 2.5gpm id say .
Advantages might be ... less weight , less current draw , which is great for me as i rum two 6.6 on the same cord as the pump .
Diagraphm pumps need no priming before u start , can run dry .less fussy in general .
It works for me anyway , if just detailing with my single jet wand or doing upholstery the single pump if all i need , but if i have to relly flush something bad the second pump makes all the difference and you use larger flow wands without the pressure drop at about 200psi .