Dripless moldable packing
on the PSS system, a tear in the bellows can sink you. I have a friend who went below to find his bilge starting to fill up. He has since gone back to the traditional.
Myself, I have a PSS, but every 4-5 years one needs to replace the bellows while the boat is on the hard. PYI sells these fairly cheaply.
The PSS system is good, but it too needs some maintenance including being burped whenever the boat is put back into the water so that the air pocket is removed.