I was satisfied with the results most of the time, even though it took some time to take 20 or 30 images at different focus distances
(automatically, thanx to the Focus Bracketing feature of the Mark II), convert the RAW files to DMGs then feed them into the stacking software.
So when Olympus announced a firmware upgrade for the 12-100 f/4 a short while ago, I didn't bother trying the in-camera stacking
that formed part of the upgrade -- until today.

The left image is the one made by the out-of-camera method (30 RAW shots, converted to DMGs and fed through the stacking software);
the right one was done in-camera. Although a little bit of cropping shows in the 8 in-camera images (most evident in the lower right
corner) I think the in-camera image compares very favourably with the 30-image out-of-camera version. As a side benefit, the
resulting in-camera image is only about 3/4 as large as the out-of-camera one. (To be fair, the version of the out-of-camera stacking
software I used is quite dated; it's entirely possible that an updated version might yield files of comparable size.)

Best viewed at original size.