As I said, the DL firmware does not yet have all the optimized writing strategies of the other currently available firmwares. It may work perfectly for you, but in general you will be more likely to have more issues with certain types of media and playback issues on certain machines.
I have this drive and when DL media hits the stores at a reasonable price (less than $13, I hope), I will give it a try. There isn't any legitimate reason to be using this firmware at this point, unless you just want to try it for the heck of it.
I've had this drive for a few months now and have been following the discussions in the NEC hardware and firmware forums and testing various firmwares to get the best results on my media. If you read the discussions on this DL firmware, you'll see that no one is getting better results on standard single-layer media using it. They're getting worse results and in some cases the DL firmware causes other problems. Most people who try the DL firmware for "testing purposes" or just for the heck of it revert back to one of the more mature, optimized single-layer firmwares for everyday burning after their tests.