OK now, after a couple of days: No bugs so far, very fast and it just works. I have tried all possible configurations and combinations within my 2 (sometimes 3) - devices via airport express and via cable.
All the problems I encountered were due to a bad NW setup (my fault) and/or to the existing macbook pro airport connectivity problems (which are meanwhile wellknown, beside Apple, who continues to ignore it …). Synch pro is acting as good or even better as the finder (sometimes i had the impression that it was ways faster; but that, probably, was just an impression)
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The price was a bit heavy, but there are no alternatives. (for backup-/archiving-only purposes I recommend Apple’s "Backup". It’s free and the last version (3...) is really OK. finally ;)