I picked up this Omega 2538.20 over the weekend (otherwise known as the Omega Great White).
Before going for one of these I had done a fair bit of research on the model and on one forum had seen it described as a 'poor man's 16570'.
Rather unfair I think, putting it next to my 16570 it's hard to decide which one I actually prefer.
On the inside it has the Omega cal 1128 movement with independently setting hour hand. To the purists, this may be inferior to the in house Rolex movement, but it is robust and achieves compliance with chronometer specs with ease.
On the outside, I like the enhanced size compared to the Rolex, probably somewhere between the 16570 and the 216570. With its white wavy dial, 300m water resistance and a price tag less than half that of the Rolex, what's not to like?