The 1.1 GB update starts its rollout in Australia soon after the 9.7-inch Galaxy Tab A received Marshmallow as well.
http://www.notebookcheck.net/Samsung-Galaxy-Tab-A-8-0-gets-Android-Marshmallow.167853.0.html
Ok, I had a Nexus 7. When it updated to 5.0 it became slow and useless. I just got the tab a, and really don't want to suffer the same experience. 5.0 works great on it, nice and fast. So I haven't done the upgrade. Waiting to hear from people who have. Will love to hear from people on what they think of it.