The front compressor wheel is not 'plastic' it's 'bakelite'.
This gives the turbo faster spool. There is no problem with running more boost on the sII turbos. The front wheel never has a problem.
It is always the rear ceramic wheel that lets go.
Furthermore, once the rear wheel on turbos let go, the front wheel usually loses its balance and will eat the housing.
The bakelite compressor wheel will supposedly also do less damage than a metal compressor wheel.
Lastly, the sII turbos are newer, so are generlaly in better condition.
therefore, in summary, the advantages are: faster spool, newer, less damage.
No disadvantages compared to the sI turbo.