For 349 USD and 5 days to go, I'll pass on it.
It's not that rare (R5 at Peter Kitchingham's lens site); much rarer is the late black version. As with some "rare" items it can be questioned why it was sold in those small numbers although offered for more than a decade. From what I've seen it's one of the weakest CANON RF lenses. The older 28/3.5 is more common, offers better performance, is cheaper to have and even smaller.