At the time, I guess I felt that with multiple units requested anyway, it made more sense not to have equivalencies (otherwise, why is one bothering anyway to ask for multiple units). But thinking again now, you're probably right that this was an oversight, so would suggest to adapt the documentation to what the code does with your change. 

I should perhaps add that I'm not quite sure what the point of this ability is -- we do not use it anywhere. I think it would be fine to tell people to do `any(unit.is_equivalent(other) for other in <some-list>)`.  But I similarly wonder why `to` would allow the ability to pass in lists (without it, we could omit the whole `_condition_arg` and gain quite a bit more speed), but such issues are outside of the scope here.