I’ve used Garmin satnavs now for 10 years and have always found them to be accurate and trouble free. The frequent updates mean that they are mostly far more up to date than many in car units.
I also like the way I can preprogram a route using my computer and Garmins Basecamp software. That way I can determine the route that I wish to follow. However on arriving near to a site I always follow the sites own instructions and do a recce using Google Earth Streetview.