That picture isn't fair - I have another one shot with a different rear cell of the same focal length, same front cell, which is perfectly sharp from corner to corner. Unfortunately the box I kept the negatives in leaked light (which you can see at the top of the "comatose" picture), and that negative looks really really bad.
The tradeoffs are:
Somewhat poorer performance since the cell spacing is fixed for the whole set,
Limited max aperture for the longer lenses,
you need a conversion table for the aperture (except the Polyplast)
Noone has made one for at least 50 years (with the exception of Ron Wisner), so it will be old and most likely uncoated.