A resonator is good enough if you stick to Low Speed (the 1.2M-bit mode).
Good enough for a mouse, apparently.  Historically, resonators aren't good
enough for Full Speed and up.  This probably means that for hobby use, you
might get lucky, but if you build several of them, only some of them will
work. Or sometimes they will work.

I've had a few USB devices that occasionally drop off line, and suspect it's
related to a not-quite-close-enough clock generator.
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