I finally got the chance to see a MK25/S600 titanium today with my own two eyes (Scubapro rep brought it over to Guam). It is a sweet looking reg. According to him, ALL the parts (except for the piston) are pure titanium in the first stage, and the second stage has titanium trimmed face plate, and titanium demand lever. Now...I could have gotten the names wrong (NOT a repair tech) but thats what I think he said. Oh...it also comes with a new "softer and more flexible" hose, an allen (?) wrench, and a cool little padded bag.
Now, does this make it worth hundreds more than the non-titanium reg? In my opinion...no. (hope the rep isn't reading this!!) As long as you take care of your gear, any brass reg should last through your diving career (or at least until the new toys come out!!)
One good thing. The MK25 is replacing the MK20, so the price is still the same. Once the warehouses run out of MK20s they automatically start shipping the MK25 for the same cost. Don't know if this is going to last...so if you want the "newest" for the same price, I would get it now!
However, we were warned to tell customers NOT to touch the external adjustment. That was put in for the conviencence of servicing by the repair techs...and not for the average diver. It makes adjustments easier and quicker.
But whether you get the MK20 or the MK25, I don't think you could go wrong. I've used the MK20 (but Santa brought me a MK16/S550...which I also love!) and it is basically bullet-proof!
But....please don't test THAT theory...isn't covered under the warranty!