SBOX and AR 2 v2 questions

[Chrono]

Ok first, I've ordered an SBOX USB mod and I'm wondering what it can and can't play. If anyone has one please tell me of your successes/failures with it in conjunction with an AR 2 v2 or GS (I imagine the compatibility would be the same).
Secondly, everywhere I look I keep seeing stuff about NTSC users to use a GS and PAL users to use a AR. I have an American PS2 and I ordered an AR 2 v2 for it from www.lik-sang.com. It was clearly marked "For USA consoles" so why do all the tutorials say to use a GS if you have a USA console?