I would be very suprised if anyone in the UK owns both complete sets although they may own a combo set. It is the sort of question to ask on the golfwrx.com forums as some americans seem to buy more sets.
There is an option on the Mizuno site to compare the 7 irons in 3D which may give you some idea:-
https://golf.mizunoeurope.com/golf-clubs/jpx919-series/jpx919-forged/919/#irons-index-hmx go to the bottom of the page and click on "3D model view" you can then select 919F and MP20 HMB and manipulate the image through 360 deg
There used to be an iron comparison table on the Mizuno site but the link now takes you to the 921's and MP20's
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