Sony's old made in Japan 6x (NN3) BD-R discs were fantastic. In my experience they're in the same class quality-wise as Panasonic and much better then FTI.
But I've never used the 2x discs. As always, the best way to answer your question is to sear the forum and see what scans other people have posted.
Regarding the price, their value depends on your circumstances. DL discs don't come cheap, especially the DL RE ones. I find the latter extremely useful (they fit my system partition images & VMs on a single disc), but if SL discs will do for your needs they're much more economical.