i'm looking at the dmt diamond stones and i can't decide which is the better one to get

would you rather have an 8" DiaSharp continous diamond stone in either 220 or 325 (only one)

or

the DuoSharp 2 sided polka-dot diamond stone with 325 and 220 grits

the duosharp is only slightly more expensive ($7.00 more) Is there a difference between the two other than the diasharp cutting a little faster because of the extra diamonds. The diasharp uses a steel plate as a core, what does the duosharp use?

the stone will be used to lap other stones