Don't use that installer. He's clearly a liar.
I'll be testing a Magic 3.1 very shortly against Messiah 2. The Magic 3.1 is reported to be a vast improvement on the Magic 3.
The bottom line technical difference bwetween the Magic line and the Messiah line is boot strategy. The Magic line assumes after 3 cycles that the game is ready to boot (which may not be the case if it has difficulty reading because of poor media or dirty lens). messiah 2 properly reads the PS2 status and doesn't kick back in until an appropriate PS2 event has occurred.
Your installer won't have a clue about these things and is only interested in selling you what he has (understandably). But lying about DVD9 is very bad. Magic 3 NEVER booted DVD9 (3.1 may well do so now - I;ll let you all know).