I run two Di622's but they are canon mount, so I can only use them as optical slaves in manual.
I find them very easy to use and I know nothing about flash.
Just set the power you want on the back of the flash, pop up the on cam flash to commander and fire away.
I am thinking of selling them and buying the Nikon versions, as it would be handy to have Ittl when on camera on the odd occasion.
The build quality is fine, no complaints at all. Only 2 buttons, so very easy to set up and use.