I used the Mobula extensively yesterday and had a LOT of fun, especially against other mobulas. The biggest threat so far are the squids, because they can run circles around mobulas, which just sit there taking a lot of carronade/flamethrower damage from below.
Basically, the gameplay with the mobula is: kill your enemy before it deals enough damage. And it _can_ do it. I had 2 gats and 2 flaks firing and enemies just died in seconds (yes, I was firing too). With less health than a spire, once the armor is down, it's game over. That means that you have to be able to do the same to your enemies, killing them as soon as their armor is down. This is the true glass cannon, much more so than the spire, in my opinion.
I, for one, am satisfied with the ship, and my crew said they had tons of fun. Nobody complained about "not being able to see the fight outside", because my engineers were shooting most of the time, running inside only occasionaly. With the proper loadout, the crew is going to have a great experience.