Old houses with plaster/lathe is a large percentage of our business. If the house is empty, angle grinder is the only way to go, fast and neat. A bit different if occupied, like Reno said, lots of prep, tenting, and one guy to hold the shop vac close while the other guy cuts. The multi tool with the carbide blade does work, but does not last long especially in harder plasters. If the lathe is wood, we cut out the plaster first then gently saw the lathe with a drywall saw. It is very soft and cuts surprisingly easy. The lengthwise pieces can be snapped off with a pair of channel locks after the sides are cut to the desired break off point. We always try to be up against a wall stud, and remember to saw the lath on the side away from the stud first while it still has support. A tiny carbide bit finds the studs, and the holes it makes are easy to patch.
When my multi tool blades get smooth I cut more teeth in them on the band saw. They are only good for drywall after that though. I cut the new teeth all the way around on the straight blades, making them into sort of miniature crescent blades, makes for easy drywall cutting.
