I don't have any other strobe experience to compare it to, but I've got an old, used DS50 that's still going strong (picked up on ebay). I think the only difference between the DS50 and the DS51 is some updates to the TTL circuitry for the newer Ike housings - I use mine with the "EV Controller" to sync to a point and shoot's internal strobe right now though.
As Dave says the AA's are great, especially if your camera takes them too. The strobe electronics are seperately sealed from the battery compartment, so in the case of a battery flood just clean it out, pitch your batteries, and continue with fresh. The back door uses a flat, exposed seal o-ring design that's pretty easy to keep clean to me (the oring is 'glued' into the door, so its face is easy to clean and lube as it's totally exposed, take some of those little foam makeup application 'swabs' to clean the inset facing surface on the back of the strobe body when needed). The design of the door is such that if you grab the back end of the strobe to help reposition it, you're not likely to accidentally go grabbing at the screw or in any way 'test' the seal (I've heard some people report grabbing the back of the Ike 125's to reposition lead to a flood, but that's entirely internet hearsay, no personal witnessing on my part. And I'm still aiming for Ike DS125's for my next rig.).
It seems to charge nice and fast for the next flash, especially when you're not dialed up at full strength. And it seems to get a reasonable number of flashes out of the typical 1800 - 2000 maH rechargable AAs, good for like 2 dives and 80-100 flashes before a swap.
If I had one complaint it's that the little 'retaining ring' plastic jobbies that help hold the screw on the battery compartment door kind of get torn up by being pinched against the threaded rod inside the battery compartment. Once you lose that (mine broke off) when you undo the screw on the cover sometimes it comes 'off' but the cover doesn't, unless there's a little positive pressure inside from the batteries warming up or something. I'm assuming I can get those little plastic keeper-washers from Home Depot or somewhere - haven't really looked yet. Also when you dip-test the strobe (suggested!!) the crack around the battery door tends to bubble out a little bit since it is kind of deep, and that can be scary wondering if you're just clearing out the airspaces 'outside' the o-ring or actually leaking thru. Fun to play mind games with yourself that way.
The shots in my (admittedly abysmal, novice gallery, linked below) were taken with a single DS50 attached to a Canon A520 (4MP) camera all on the same trip at usually 60 feet and deeper in middling (50-70 foot) visibility, and mostly in cloudy conditions topside to boot. That was my first time shooting with the strobe. Judging from the shots already in your gallery you'll do much better!