Well, if you are happy wit the magic rack and all you play is 9 & 10 ball, then there is no reason to buy ANY other rack, including the Delta. But if you play any full rack games like 8 Ball, Straight Pool, or One Hole, you will need something unless you plan on racking the balls by hand.
Even if magic rack came out with a full rack template I think it would cause some interference problems 15 balls on the table, especially with the break shot of one pocket and straight pool.