I have owned both the MIO 505 and the Garmin Edge 1000. I returned the original Edge 1000 because of all the issues in May. I bought the 505 - upgraded to Version 4 - and was pleased with the way it worked. The odd distance and speed problems but BT and WiFi worked really well. Living with the 505, however, became more difficult. Garmin owners are used to temperature being recorded as part of the upload file - the 505 does not. Garmin users are used to being able to set accurate wheel circumference - 2096 for 700c x 23 - the 505 cannot, you can only use 210 cm or 83" not 2096mm or 82.6". Garmin users are used to gradient displays using decimal places - the 505 cannot, it is either 1% or 2% not 1.7%. Temperature display is the same - decimal places on the Garmin - integers on the 505. Garmin users are used to distance in miles and ascent in meters - the 505 cannot do this. The Garmin records every second - the 505 every 2 seconds. It is bizarre to watch your ride time jump in 2 second intervals!!! I kept the 505 for 2.5 months but have now returned to the Edge 1000 with latest firmware. 2 weeks in the Pyrenees later I can declare it all works well.
I lost money getting to here but I feel I can contribute to the "comparison" debate. (прям вторая Веломания) The Edge 1000 is the more professional of the two. If accuracy is important then avoid the 505.