As mecha fan, I'd like there to be a lot of good mecha games, but there aren't many. Battle Unit Zeoth is definitely a mecha game, as you might be able to tell from the Macross knockoff main unit design, but it is not a good one. It's pretty much a straight up side-scrolling shooter except that you can shoot in four directions and apparently the direction the screen scrolls changes after each stage, not that I'd ever have the urge to play it enough to be able to finish the first level.
I didn't think a game would make me rather play Burai Fighter, but at least in that game you could easily move because you didn't need to repeatedly press jump to fly and you could shoot in eight directions instead of four. I guess in it's defense, Battle Unit Zeoth is a Game Boy game and Burai Fighter is an NES game. Actually, there was a Game Boy version of Burai Fighter, so you should just play that. Or better yet, the Game Boy Color version that came out like eight years later. I just can't think of a good reason to play Battle Unit Zeoth.