Thanks for the replies guys.
I think it is a good point that usability is the most important factor.
From the Ikelite site I couldn't find a list of the available functions when inside the housing, on the Aquatica site they list all available functions.
Do you think it would make a big difference having 2 x DS-125 strobes on arms, I can understand the concept of illuminating the subject evenly to not create shadow and also having an extra strobe would give more illumination power, are there other factors?