Greetings
I certainly can give you an opinion on some of the knots you are inquiring about but it is just that, the opinion of one man and I have to declare straight away that I am not very fond of stiff inflexible synthetic knots, irrespective of how soft the fibres are.
My favourite synth. knot is the L'Occitane Plisson because it can be easily be mashed onto the face splaying the knot open, the knot has soft fibres but it is flexible. The knots in the actual Plisson brushes are not the same knot, they are very similar but are a little bigger in diameter and a little stiffer but are also IMHO superb.
My second favourite is the Cashmere knot this knot has the softest fibres of all that I have tried and it too has a decent flex so can be splayed open with only gentle pressure, this is not true of the Tuxedo knot it is a good deal stiffer and less flexible and thus harder to splay the knot without using undo pressure.
I have a couple of Muhle (latest generation fibre) they are the best and neatest constructed knots but for me a little too stiff the fibes are soft on the face, in fact all of these knots have soft feeling fibres it is all about flex whether you like a lot or a little, for me a stiff knot is also super springy and flicks lather everywhere and just will not 'mash.'
Whipped dog are good knots but again too stiff for my taste.
Razorock Plissoft knots are superb in terms of value and performance they are my third favourite it is easy to see why they are so well regarded, the fitting of some of the knots is a little suspect, I have two that have not been set into the handles quite straight but I may have been unlucky, if these knots flexed just a little more they would for me personally be perfect.
The only synthetic that I have tried that I found unusable was the Frank Shaving Pur-Tech it was so stiff that I thought I had purchased a stenciling brush, however it should be said that if you paint lather on your face and do not mash the knot the stiffer knots will work just fine.
Regards
Dick.