These things have been around the medical business for years since originally being designed as bone saws. Their claim to fame has been that they will cut something solid like bone but will just harmlessly wiggle something like soft tissue...and they're easy to control. If the blade suddenly gets caught in the cut you just let the tool wiggle as it stops whereas something like a sawzall will start bouncing the whole tool around.
Any blade with teeth will cut the plaster (it's quite similar to bone) but if the teeth grab the metal lath it will grab it and start shaking it around. You can use it (carefully) with wood lath because the wood will cut similarly to the plaster itself; but it's a whole lot trickier to do the same cut if you have metal lath.
I would suggest practicing somewhere out of the way like an inside wall of a closet before using it on a finished wall. You might even want to make a sample piece of wall to play around with using some scrap metal lath and plaster patching compound.
