To further back up my earlier comment “these are dark days for us underwater photographers” is because I love all the moaning about how strobes are not as reliable as we think they should be. What is obvious, most, if not all don’t know or have memory of how it was back in the earlier film shooting days where your choices in underwater strobes came in the following flavors:
1. If you wanted to shoot wide-angle, the dam things were often the size of a coffee pot - think back to the old Ikelite 225 to 300’s or better yet, the Subsea Mk 150. Smaller strobes were only good for macro.
2. Most came with only one to two power settings – full and maybe ½ power, with the slightly more exotic featuring ¼ as well.
3. Sync cords: Most were not user replaceable and were highly prone to internal breaks right outside the bulkhead on the strobe. A common solution to create a strain relief was to wrap it with a s#%t load of electrical tape. Then there was the housing interface comprised of either Nikonos II or III bulkheads, or the wet connects comprised of EO and Sea Loc. All of which were true PITA’s.
Are our current strobe choices perfect? Hell no! Anything with electronics that are going into a marine environment is going to fail at some time, given the fact that anything electrical is deathly allergic to saltwater.
While I enjoy the fact that todays strobes are smaller and lighter and thus far more suitable for travel than those monsters of yesteryear, which some would rival the size of todays mirrorless housings, you should not place expectations that they will handle the work load of pro. The flashtubes in these mighty-mights work pretty well, but they have their limitations, namely because they were designed and built (Sea & Sea’s D1 and D2 are the first to come to mind) for the hobbyist market.
It is for the same reason professional fashion photographers use large monolights instead of on camera flashes that run on AA batteries.
I look at this way. If you are a moderately serious shooter, you invest in two. More dedicated shooters certainly three. As for the Pro (and those who think themselves a pro) you travel with at least four our more - redundancy is the mother of backups.
No one ever said underwater photography is an inexpensive pursuit, so be prepared to pay in order to play.