As someone has pointed out in the post's comments, there's the Wombat ADB-USB converter as an alternative. Doesn't look as good, but requires no battery or other power supply. IIRC, it does distinguish between left and right Shift/Command/Option keys. Quickly looking at the product page I realize that it even converts both ways, so you can also use it to attach your USB keyboard to your ADB Mac or NeXT.