I do not have the micrometer type seater, but am thinking about getting one. My conventional RCBS seater requires quite a bit of fussing and several small turns of the stem to get the OAL where I want it. Measuring after each adjustment, of course. Once I get it right, if I lock up the stem good and continue using the same bullets, it stays good. Once you change bullets, of course, you are back to tweaking again.
The micrometer seater would simplify and be more precise. Problem is, the micrometer seater would cost more than the entire standard die set! Only worth it, I think, if it is used with a caliber that profits with accurizing details, such as a BR rifle or vaminter. For a hunting rifle just used for some casual shooting, unsure if that level of precision would be worth it.
The only reliable OAL measurement would require a caliper used with a bullet comparator device. That's how I do it.