Plasmon is this really Plasmon themselves you mean. Since PLasmon sells there technology to a lot of third parties. (just like DST most disc's that are recognized by ATIP only as DST here in Europe aren't made by DST themselves. )
Now Plasmon themselves are good.
The third parties like
AOD (Double Diamond Digital),Euro Digital Disc, Intersonic S.A. ,DCD Line Ltd., Care4DATA group (if I'm correct) and some other factories.
Now some of those are very good while others are quite bad.
If you can give me the brand of the disc's then I sometimes can retrieve the manufacturer and say something about quality.
Prodisc - there okay, don't expect very high quality but most of there stuff is fine. However there are some people who are haveing problems with the newest disc's of prodisc's own brand. The media seems to have some bad problems because of the shape.