Garmin Foretrex as backup gps unit

https://buy.garmin.com/en-US/US/p/30026

Anyone have experience with this unit? I want something that will be my backup in case the chart plotter fails or loses power for any reason. The etrex 20 and Garmin Oregon look nice and everything but like I said this is a backup. I really just need the most simple, reliable (marine resistant) device to get me back to a way-point/whistle buoy/harbor entrance/etc. This looks like it is very utilitarian and gets high reviews on every site I look at.

Another option is to use a phone in a waterproof case as a backup. The app Gaia GPS lets you download NOAA charts beforehand so you don't need cell service. Navionics also has a nice app but Gaia GPS also works with topo maps for hiking so I only have to buy one app. As an added benefit, I record every trip so I have a record of where I went, how fast, etc. That syncs to the cloud so I can look at it easily on my computer after the trip. Easier than trying to get that data off of my fish finder.

Following. Looks like a cool unit. I have been using the etrex20 for... 8? 10? years for backpacking and kayaking. It has its quirks but it's been dunked and rained on and slammed around that whole time and is still going strong.