Bill the downside just like the P30+ being they use the same sensor it is a generation older . So in comparisons to the new 6 micron sensors it is slower shooting, it has micro lenses, it's a kodak sensor and your buying a older technology which is not a bad thing. Just that you are a step behind, but these sensors have been the workhorses in the rental , fashion industry for a long time and they produce a great file.
The new sensors are faster shooting, 6 micron , Phase has no micro lenses and I think Hassy does . Phase is Dalsa , Hassy is Kodak they will produce less moire than the 31 mpx and they do produce lower noise in the higher ISO's and the are the newer breed and worth more in resale.
The 31mpx is a great entry level now and getting in the door is easier to do because both Hassy and Phase the 40 mpx is the latest backs.