It is illegal to own and use one as a private citizen for self defense in my state. I own one because I am a guard and have a baton license and you need to show your baton license to purchase one. Other than without a side handle the use is the same as a regular one in terms of technique. If you know how to use a stick or walking cane for combat you will do fine with a baton, or rather, if you are not allowed to carry a baton for self defense, some form of stick or walking cane is the substitute you need.
Yes, a baton can cause potential fatal injuries. It is only used for compliance through pain. You can break someone bones easily. In general, if you are licensed to use one, you are really confined to use it on someone's limbs, and due to close proximity of arms to chest neck and head, probably confined to use it on someone's legs. Wrongly using it is a felony so you treat it just as serious as a firearm. If you were forced to use one you really need to file a blow by blow report in order to make sure you will not get sued.