A vernier will do that, but to be honest if one needs trimming they probably all will. I use STM tumbling which, combined with a Forster 3 in 1 trimmer means the case mouths can be slightly battered after cleaning, so I always trim (tidy up) on each reload. Its a de-burr with brass being removed if it has flowed a bit.
Even with 100 at a time it does not take long. For what I do I would never measure every case, however if you are F/FTR/BR based then yes, but again why not just use a decent digital vernier? You are not actually measuring COAL, but case length (Head to mouth) which is probably where the confusion on my part came from.