It works!

Fine App with komfortable functions and GREAT support by the Developer.

For all with the BT Connection error, here is a workaround:
1. Launch MapsGPS and hit connect just once (it will not connect due to the bug, but the app will now try to reconnect later on)
2. Go into Settings->Bluetooth on the phone, select the classic BT connection (the one without LE), and hit the little info symbol, then hit disconnect
3. Go back to MapsGPS (easiest is to double-click home), and hopefully it has reconnected.

ShinMuso about MapsGPS for Pebble - Smartwatch maps and directions, v3.0.1