I use a cheapo one from Brownell's and my measurements have been confirmed on Hosford or similar gauges. I simply allow the gauge to flex vertically before/while zeroing the gauge.

The measurements don't need to be precise, I just need to know within a few thousandths what I am dealing with. The thinnest I have seen so far was my 12 proved 10 gauge that had been hogged out to a .783 bore. Still had .021 at the thinnest spot.