Different. Grinding guards, or night guards, try to give you something to grind on, to destroy plastic instead of tooth. Problem is, the damage to muscles and joints is not eliminated and grinding can get worse. Splints try to reduce symptoms (pain). Some can even stop grinding.
No. Tmj splints has a specific purpose. Grinding guard has its own purpose.
Yes and no. There are many types of splints and night guards. Many are multipurpose. Make sure your doc is a true TMJ expert.
Basically yes. They are basically the same but the precision of a well made splint is what is important.
Options. Do you also grind your teeth at night? Clenching occurs during the day. A lot depends on the the history and diagnosis that you have received for your tmj/tmd. An oral mouthpiece may be indicated, but there are many types and often are constructed based upon diagnosis.