The thing to remember about micro bubbles (or any bubbles for that matter) is that they are AIR.
If a micro bubble launches into the water, and say lands on a coral. That part, however small, is now in the open air.
If a bubble wand was to put say 30 micro bubbles on a small area on say, a bubble coral over time, the areas with the bubbles are now, for all intents and purposes not in water. Which from what I have heard, is very bad for bubble corals.
Thats what you need to consider...