I am using the GNS1000 on a APPLE iPAD
with Navionics Software
. So I can answer some of your Question regarding the GPS, but not regarding Open CPN.
I discovered that the GPS device is working just great on speeds above ca. 2 knots. Below this speed (exactly 1 m/s) the developers had build a threshold to prevent the device from sending skipping positions. Instead they send a position only when it changed 50 to 100 meters. According the support of GNS this is done for automotive and avionics users.
For us sailors this is bullshit!
we cannot use it for anker watch. And we cannot use it for speeds below 2 kn. For hikers and geocashers it is also not helpfull to get a position only while running ;-)
I am also looking for an alternative. It seems GPS developers copy this feature from their competitors, because other manufacturer have the same bug. I am interested in other peoples experience. Please tell.