No idea about GDI. All I know about those is that they are crazy expensive.
Bobro makes some of the best mounts in the idustry, and those are about 1/2 the price of the GDI.
http://www.bobroengineering.com/
They are auto-indexing, that means no adjustments necessary. Fits out of spec rails too.
A cheaper, but still very good option is ADM (American Defense Manufacturing).
http://www.americandefensemanufacturing.com/
Really good QD mounts. Not auto-indexing like the Bobro, but that is really not a big deal because they can be adjusted without tools. They also accommodate out of spec rails.
The Larue mounts are quality, but don't do as god a job at accommodating rails that are out of spec, and some people don't like that they can mar your rail. Also, adjusting them requires a hex wrench.
