Wait why is there a vertical gap between the Barrels?
Space is reserved for ME Storage Bus.
In that case, cant you have two Rows of Barrels before you need one Row of ME Cable for 2 Storage Busses?
Of course I can. And it is a simplified design coming from which has a hopper under the barrel. I use this design for advanced dust processing. If I change the constructs to what you said, something must be discordant(I think gaps are necessary :)). Rather than saving space I would like to wasting resources to ensure compatibility.
You know that tiny dusts in dust barrels will accumulate to full dusts without needing a dust funnel to do the job for you?
Also the Barrels do have Auto-Output capabilities towards the Bottom Side. 
Yes, I use this convenience to collect all kinds of given out by the Large Shredder and the Large Centrifuger. Barrels’ auto-output mode is useful but what I actually need is hoppers’ exact-value-output mode. I will need it for dust-processing because centrifugers’ and electrolysers’ dust-processing recipes need precise amount of dusts. So I have to use hoppers but not barrels only.