I have the Series 4000 UWA, in the 14mm. I have also previously owned the 6.7mm UWA.
The 14mm UWA is a superb eyepiece, but very heavy and can introduce balance issues - but they are very easy to solve.
Glenn Dawes and some other observers loved the view through my 14mm UWA on Saturday night. They still attract a premium on the 2nd hand market (usually AU$200+), but they hold their value well and are now a bit of a collectors item
I have no experience with the s4000 plossls, sorry.