Ah, something I can comment on at last - I have both
The Pro 750 also sits around the ear, and is in the same sort of price range, but that is where the similarities end.
I've just bought a pair of the standard Sony silver 1r 'phones, and have only had <3 hours listening so far, so keep this in mind before considering my comments. The 1r is much warmer/more euphonic sounding than I expected, which is not a signature I've come across before, but I like it. I expected the warmth to mask detail a bit, but it doesn't. I'm still forming an opinion, and need to get used the new sound signature, but I certainly like what I hear so far.
I also own a pair of Pro 750s, and to my ears I don't think the sound signature could be more different between them and the 1r. I should warn that I'm afraid I don't like the sound signature of the 750s as I find the top end too harsh and the mids seem to have a slightly phased effect which makes the mids sound odd for some of the material I listen to. The Pro 750 sound grinds me down quite quickly, and I subsequently end up going back to my other 'phones. I do like the bass on the 750, but it's not enough on its own to compensate for the upper frequencies for me. The 1r has a more pronounced upper bass, whereas the 750 goes lower. So far for me, the 1r is a much more enjoyable 'phone than the '750.
For context, my ears have become rather used to the Denon AHD-5000, which has quite a different signature, and more recently I've been listening to the JVC HA-S500 at work. My taste in music tends to go from electronic (techno, deep house, ambient) to jazz (John Coltrane, Dave Brubeck, Miles Davis) and piano music (Nils Frahm).
Your ears may vary of course, and all usual disclaimers apply
I hope that makes sense and isn't too muddled - the festivities have begun!