Thank you all for your input.
Next season we will be using a original Flarm in our Husky A1 tow plane (located in the Netherlands) with a butterfly display. Depending on our experiences we will later decide on the upgrade to a PowerFlarm with ADS-B. We already have a mode-s transponder with ADS-B out capability.

In Europe we have rather different results with the range of the Flarm RF signal.
Overhead dense populated area's the results of a Flarm range analyses go from average to poor, while flights over desolated area's like the high mountains of the French alps give excellent results.

Here you have a range analyses of a flight with a DuoDiscus with original Flarm plus dipole RF antenna overhead the French alps http://bit.ly/UbXQvu

This is a range analyses of the same glider with the same Flarm equipment during a flight overhead dense populated western Europe http://bit.ly/VQxBXQ

This indicates that the correct placement of a high performance Flarm RF antenna is very important