I am one who takes apart even new kit, including the Mitutoyos.
I do get it that a whole lot of effort making something like a kit reworked up to "good" is not what we really want - but that is only if the rework is significant, amounting to a real bummer disappointment to have to do, and knowing that in the end, the basic kit will never perform. In this case, the effort is minimal, and very well worth it. No amount of rework TLC will ever make the junky eBay calipers OK, but not so on those that can end up excellent. Mine took about 20 minutes each.
A new iGaging can be made great with very minimal work, and a small 3" x 3/4 slip-stone. You don't need a set of ultra-fine abrasives. You need only give a little attention to the edges you might touch, and exterior edges, taking care not to damage any measurement part. That said, if you have a known flat stone, you could rub away all day on a gauge block, or a caliper jaw, and not alter it's surface at all other than making it shinier. Clean it, adjust it right, use a very small amount of very light oil, and it achieves that satisfaction point. I think it was the demo by Robin Renzetti that convinced me you can take a stone to precious accurate surfaces, and not harm them. I used my 3/8" thick 8" x 3" diamond hone to flatten the stone.
