Yup, one word...unreliable. Memorex does not manufacture media. You can have vastly different results even within the same spindle. You may get lucky on some burns, but trust me, you will certainly get unlucky. Good chance they are Ritek D01 or worse.
The only consistently recommended DL media here and most forums is Verbatim +R DL.
Take a look here:digitalFAQ.
Hope this helps.