I also have an Etrex H unit that we use for the kids as we use the iPhone app.
I find that the bearing is very accurate the problem is when you slow down the compass will read wrongly.I find the best solution is to have a basic compass with you aswell. So you can check the direction.
Like I say the bearing is normally correct so if it's pointing to the cache and saying South make sure you are facing south.
Hope this makes sense