I understand people like to experience BOG for the atmosphere... But if you're doing dinner just to get to see Beast I would not recommend it, the actual food at BOG is low in terms of other similar priced options at Disney... While you are probably 95% certain to have Beast there, you will have to stand in line for him and that line can be rather long and slow, I think we wasted about 30 minutes waiting in line after we finished our meal just for Beast so know that you'll be giving up a chunk of time for a interaction that is often little more than a stand here photo and move on.
If you just want the experience of eating there you might think of lunch as a better option.