They are a great unit and will restart after a power failure. And they do basically set to what ever flow you put through them.
If you get a pump that has about the same GPH or more, (with head loss)
and put a valve on the output side you can find a balance between the flow and noise level. Most overflows can be noisy when they are near their rated capacity.
I see they they have a silencer option now (kinda looks like
Stockman's overflow box version) if noise is issue for you or the powers-that-be
.