John,
Just to qualify my answers, let me start by saying I've currently got the DS-50, and will most likely be upgrading to or adding a DS-125 in the near future.
There are pros and cons to both the -50 and -125.
The DS-50 is a great little strobe, especially when you've got one of the P&S cameras like the Oly 5050. Add the manual controller and you've got a very nice, compact adjustable strobe. Another nice feature is the fact that you can use AA batteries instead of a proprietary battery pack and charger. It's a heck of a lot cheaper to keep a spare set of AA batteries in your bag than an extra battery pack for "emergencies". I never used rechargeables in my -50, simply because it didn't go through that many batteries. In the course of 15-20 dives in Cozumel last year shooting on Full power, I went through two sets of batteries if I remember correctly.
The downside to the -50 is that if you plan to upgrade to any housing / camera combo where you can't use the optical TTL sensor or the camera doesn't shoot in TTL like the Fuji S2, the strobe becomes somewhat limiting. Case in point, the strobe worked great with my Sony DSC-S85 / Ikelite housing, but it's more limited with my Canon D60 / S&S.
The reason I'm going to add a -125 is for wide angle. The decision I have to make is whether I want to replace my -50 or add a -125 to my setup and keep the -50. The -125 has significantly wider coverage than the -50. It also has some level of adjustability built in, so there's less of a need to add a manual controller if you want to shoot manual. The rechargeable battery pack is both a plus and minus in my mind. I like the concept of rechargeable batteries, but not having used them, I'm not sure how they'll work out when diving 3-5 dives / day.
Brings up some interesting questions for the -125 users. Do you carry an extra battery pack if you only have one strobe? And do you have the normal or fast charger?
Hope this helps...
Tom