While I can't comment on the 225i version, all I can say is the 225 pretty much is the quintessential Prestige Series Grado, and if want a summary of what Grados are all about, look no further than the 225. You definitely have that Grado midrange, there's bass but not much in quantity, and of course, the issue of fatiguing highs.
With the MS2i, I feel like they're very different from the Prestige line of Grados. They have more bass extension without the fatiguing highs. And while they are considered the neutral Grado (as Alessandro's are known for), they are very different from the MS-1 and Pro. They're sound signature is more pronounced yet more balanced than the 225 (more even spread across the spectrum)
In my personal experience, I personally enjoyed both, and actually preferred the mids of the 225 over the MS2i, but the lack of fatigue and bass extension won me over