Now a days, for the most part, comparisons become like comparing a bowl of chocolate ice cream to a chocolate Sunday. Meaning, they both taste great on their own, but the Sunday just brings so much more to the palate. The underlying problem with that is it's still personal preference, some just don't like Sundays
That said, the StudioPhono is a great sounding, well rounded phono stage. Outside of the sound quality it brings, it does have a couple of great features at it's price point that you don't normally find, a mono switch and MM/MC capabilities and load/gain controls. The Insight has, in my opinion, great tonality, a huge soundstage and is just a more "engulfed" sound. It also has 50db/55db gain settings which are lacking on the MoFi, I've always found that to be a weird gap on the MoFi going from 46db to 60db, the MoFi does extend further to 66db, but I'd be hard pressed to find an "every day" reason to go that high, conversely the 50/55db gain on the Insight is kind of a sweet spot with a lot of cartridges.
The Insight is a "better" phono stage, but again, what are your needs, preferences and budget? The drawback in the here and now is you can't just go hear something if you get the itch, but if you have the funds and especially if your getting a deal, I have no doubt you'd enjoy and not regret the step up to the Insight.
As a point of reference, I've had both and they were both running on an UltraDeck.
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Oooof, that was a while ago