Big difference..... I do not need to refer to the Bible to know that Baha'u'llah was the Messiah because I have the Writings of Baha'u'llah and all that He accomplished in His mission which matches up with the Bible prophecies.
I also do not have to interpret the Bible to fit Baha'ullah; all I have to do is look at what Baha'u'llah actually did to fulfill the prophecies in the Bible. There is no Messiah Ben Joseph or Messiah Ben David who have actually shown up so it is just what Jews imagine the Messiah will be, not a reality.
Believing that Bahulllah is the Messiah isn't much different from believing in Messiah Ben Joseph and Messiah Ben David. The Bible never mentions Bahulllah coming because Jesus Christ fulfilled all of the messianic prophecies. Jesus said in Matthew 24:5 For many shall come in my name, saying, I am Christ; and shall deceive many.