I just checked this drive out and as your supplier has said there should be no problems.
It is a DVD +/- RW dual layer burner.
It depends on what you are trying to burn to DVD, Sonic MyDVD is for burning movies, slide shows etc..
What size DVDs are you using, you say Memorex DVD +R, but are they 4.7gb or 9.6gb?
Unfortunately, although the drives are now dual layer there are not many dual layer media disks on the market yet.