Turns out now it works, despite the fact that the browsing still does not give any answer from the unit.
For me it works like this

1) sudo hcitool scan (find unit)
2) sudo sdptool browse 00:00:00:00:00:00 (whatever it is)
3) sudo rfcomm release 0 (very important for me)
4) sudo rfcomm connect 0
...connected /dev/rfcomm0 to 00:00:00:00:00:00 (whatever)
...Press CTRL-C for hangup

and then on a separate terminal

5) sudo gpsd /dev/rfcomm0
6) sudo xgps

(of course rfcomm.conf is configured)