The advantages of an internal modchip are so compelling (see my reply to Cosmodk) that you should seriously consider having the PS2 chipped by a professional.

That said, a USB solution works at the cost of having additional complexity with EA protected games. Using CloneCD and a fully compatible burner most backup games will play in conjunction with Action Replay 2 as boot disk. But certain popular EA games need to be patched via a specific procedure found at ####://www.eapatcher.com

So it's soldering + trouble free backups via CloneCD versus USB Mod + more complex backups.