I use an ikelite 200 on ultralite arms. I love the strobe, but I couldn't imagine having a second. All too often I have too much swimming to do to keep up with the DM or group. Solo dives are a different story, but you need to consider the type of diving you do and how much current or surge you are typically in.
I had ikelite arms, I now have ULC. The ULC are wonderful, but I find that I keep them pretty loose so that I can always move my strobe. I don't spend a lot of time getting the clamps tightened just so. When it comes time to swim or hit the current, I hold onto the strobe with one hand to keep it from moving. I couldn't do this with two strobes on ULC arms, without spending more time getting the clamps just right, tight enough to hold, loose enough to move (silently). The strobe has enough cross section that when the arms are as loose as I like, the current can nudge it. It has enough mass (which still counts underwater) that it will stay in place if I move the camera really quickly. Perhaps I like my arms looser than most.
I love the wide angle on the 200, I just don't worry about coverage. I don't really need the wattage, I am rarely shooting it at full power. In fact, for macro, I typically have to pull it back so that it's as far as possible from the subject, even with my camera (oly 3040) stopped down and the strobe on 1/4 power. I just got the diffuser, haven't used it yet.
I like the battery and charger a lot, it's really robust. I've had mornings where I have shot 200 or 300 pictures, and the strobe still has juice. The charger is fast and handles foreign power well. I've had little power brick wall wart chargers die. However, the charger and batteries are a lot to pack.
I do find myself daydreaming about a smaller strobe, something soda-can sized not coffee-can sized, with wide angle, lower power is ok, that would run off AA's so that I'd only need one kind of charger and one kind of batteries on a trip. I'd never get rid of the 200, though, it's got great performance for it's size. Larger strobes seem to have diminishing returns compared to it.