Yes I got the case if one is using a DIGI+ HAT. Much better quality then the plastic one. Only gripe is they don't provide any soft feet for the unit. I used some Sorbothane "Isolate-it" feet left over from another project.
https://www.hifiberry.com/shop/cases/steel-case-for-hifiberry-digi-black/In my system, the RP3 goes into a MiniDSP NanoDIGI, which is the crossover and EQ for the mains and subs. It also uses a similar 5 volt power supply, so I bought two identical iPowers, one for each. There was a audible improvement in the sound, in both detail and depth, most noticeable on my FLAC files.