I have a Timber Check B350 pin type which I seldom use anymore . Have switched to weighing everything , 5 kg x 1 gm pad scale for small pieces , 75 lb scale balance with a hook for a sling for larger heavier pieces .
My experience echoes Jeff`s in consistency . Readings different by several %age points are common , and probably shouldn`t be unexpected , given the way wood structure changes near branches .
Pins bend , particulary in hard fairly dry woods , as you try to get them deep enough to give a reading . Doing that on a board may leave marks where you end up not wanting to see them .
Pins may not be long enough to go through thick bark . No experience on large diameter stuff , but would expect radial differences from pith to the new wood close to active fluid transport when checking end grain . Those differnces would change with wood harvest season .