Umm, four HDD's in 1U isn't new - and if it's a first for HP they should keep it quiet. Apple's first Xserve in 2002 had 4 HDD's (in caddies too), SuperMicro have always had a crap-load of 1U 4 HDD chassis... I'm too bored to make a longer list.

Admittedly, an HP chassis is full of plastic "stuff", strange boxy hinged metal things and no space for cables.

Like Ikea, HP are purveyors of self-assembly furniture, which more often than not, come with the wrong bits.