If your core is weak is this a good one?
Yes. Great one. It will expose left/right imbalances as well.
I like to do those heavy but you must maintain a neutral position and not lean away from the dumbbell which would be the bodies natural tendency. Also, any unstable object carried overhead, like a beer keg partially filled with water or a slosh pipe is a great way to work core muscles, as is almost anything zercher.
Exactly correct. Most people do this without being ready for it and compensate by shifting their body position.
So to me it’s not a good exercise “if your core is weak”. Because if it’s weak you will compensate and it will do more harm than good. It’s a good exercise if your core is fairly strong but you want to make it even stronger.