Oh my god! So there is a Chip that can play NTSC games on PAL???
ANSWER: Yep - NTSC originals is what you mean

So why do I need the NEO chip?
ANSWER: Who said you did need a Neo chip? No Neo chip will play NTSC originals on a PAL PS2

Why haven't I heard of this Chip before?
ANSWER: You don't look hard enough around the web, the forums etc.!

What are the disadvantages?
ANSWER: None that I'm worried about. It requires you to do a swap for backups (not for originals). NEOO4 and the up-coming Messiah are non-swap on backups.

So, what are you going to do? Give Madeira Games a call?