Hi tsantee, thank you very much for the quick reply!
Mine came in a LaCie box as well. Both LaCie and NEC confirmed with me that it actually is a NEC drive without any modifications. Flashing to 3.0.6 with NecFlash went without a hitch and you can actually use the .exe file from the NEC site for doing this. Don't forget to dump the old Firmware first, so you can go back in case of disaster. NecFlash prompts you for that.
Anyway, in the capabilities it doesn't mention DL at all, but in the Features tab it indeed says DVD+R. And I haven't got those, I bought 2 5-packs of expensive DVD-R's. I did so because the only DL disk mentioned in the drive's Medialist is Verbatim DVD DL -R. The Plus variety isn't even mentioned there. Weird...
I think I'm going to ask NEC-support about this one. I really don't feel like getting new +R disks again and besides, the shop I got these from doesn't even have them.
I could of course burn to SL, but I wanted the DL for quality. If I go that way I think that instead of burning straight from the MTR 3 folder I'll save as compressed Disk Image and burn that one. Looks safer to me. I'll report back if I get any wiser from NEC (or LaCie for that matter).