Last year I was finally able to score a nice used Criterion 2" boring head. Since I already had an import clone, I thought it would be interesting to compare.
The boring head on the left is the USA-made Criterion DBL-202 and the one on the right is the imported 2" clone from Shars. Both are attached to an R8 adapter. I tried to align each at the R8 taper just to show that the Shar's head is a bit longer.
This is the Shars head mounted in the mill and with the dial set to 20. Notice the markings on the dial: it's laser etched. This picture does a good job of showing the legibility of the dial: you can read it but it's not that great even with decent lighting and this boring head didn't see much use either. On my R8 collets, after a few years the laser etching is almost completely gone. Same with some sockets I own.
And here's a picture of a dial indicator measuring the head travel: it's moved a little over 20 thousands. So when you set the dial for 20, you get a hole that is .040" bigger. It's kind of like direct versus radius reading dials on the cross feed of a lathe, you need to know which you have or you will be in for a surprise.
Now the Criterion DBL-202 is mounted in the mill. Check out that dial as it's so much easier to read! As I get older these things become more important. As with the other head, it's set to 20.
And now the dial indicator shows .010" movement (it's also moving in the opposite direction). So when you set the dial on the boring head to 20, you get a hole that's .020" bigger. To me, that seems more intuitive. It's also easier to bore a more precise hole, since each tick represents .001" whereas on the import you might have to split the marks for the same diameter.
The Criterion has a better build quality, especially in the gib adjustments, which makes the head seem much more precise. This is reflected in the price, but I bought the used DBL-202 for the same price as the Shars boring head. That was, however, a Really Good Deal and took quite a few months to find.