Always argumentative, aren't we? Of course, I should know...

Even with slinkies, I suspect that that the pellets are still relatively unavailable. Birds tend to go to target rich environments when they gravel up their gizzards. Roadsides and gravel beaches come to mind. Slinkies are going to get caught in larger rock environments for the most part, so when they break down, most of the pellets are going to insinuate themselves into the crevices around the bigger rocks. If they do get washed into the gravel bars, they'll likely be low in the gravel.

I'm sure it could happen to become available for the birds, I just don't think it's a serious risk. Besides, I mostly pull plugs.