Hi, this is not a region thing at all, they are different standards, both write once (as opposed to +RW/-RW which are read-write)supported or championed by different manufacturers and are not always compatible between drives. It depends on your specific drive but the front of the drive normally indicates what type to use (if not the manual will).

Data capacity is similar with all of the disks.

No, haven't seen any dual layer disks but haven't actually been looking....