There is this post here from many years ago: "Hidden" Vowel Filter Device!
and I recently talked with someone about it.
On the same note, I think from a user perspective it would be better to have only one filter device, then be able to select analog or digital or any kind of filter type within that one device.
So why not clean that all up and just make a single filter device with all the options.
Digital, analog or “hidden”.
I think that would be a good improvement over hopefully little work.