The predecessor of the TS-L632D, the TS-L632B, tended to burn with PIF spikes and with high jitter. Disc type support was poor. The overall burn quality was acceptable, but not really good.
I don't know whether Toshiba/Samsung fixed these problems this time...
Plextor's burn quality is not the best anymore either, the PX-755 and PX-760 were messed up. I would recommend you getting an external 716 if you can - the non-716, non-755, non-760 externals are relabels
What about an external LG? These do have great burn quality.