Hi Blackfire1967,
I’m afraid we won’t be able to find a meaningful answer because nobody so far posted anything about the durability of the new plastic freewheel 
So nobody knows…
For the aluminium version I’ve memorized a negative record of ~ 1 200 kms but on the other hand reported some riders of 8 000 or even 10 000 kms.
I bet there must have been at least two different versions on the market back then; some were obviously much more bad than others (perhaps caused by insufficient treatment of the aluminium surface). The huge discrepancy can’t be explained by external influences (mud and rain) alone I’m sure.
However - the more you ride in rain (and the dirtier your roads are) the sooner will the freewheel wear out.
Btw; several European companies do not offer the new plastic freewheel;
I couldn’t find it neither at Strida Germany nor Netherlands, Denmark or Italy.
At Strida France it seems a bit overpriced (as usual).
Cheers,
Chris