As far as i can see, having looked at both 3500 and 3520 write strategies. It appears NEC have taken the 2.18 ND-3500 and used them in the ND-3520, added a few RW strats and the -R DL strats.
I guess they needed a starting point, but the hardware is different. So what worked for the ND-3500 needs tweaking for the ND-3520. Of course as Code said, maybe the hardware isn't so good. But its not bad either. I think when NEC put some effort into the firmware on the ND-3520, the drive will turn out to be a good drive. It will have to be good, as i think this new hardware (chipset) will be used for quite some time by NEC.