UPS or Universal Polar Stereographic is used in the polar regions north of 84 deg. and south of 80 deg. It is based on a polar stereographic projection tangent at the pole. (Picture a radar scope centered on the north pole.)
From a users prospective it's still a square grid measured in meters. Should you end up in the poles, you'll find using UPS seems very much like using UTM.
Setting your Garmin to display UTM/UPS is what you want to do. It will switch between the UTM and UPS regions should you happen to wander into the polar realms.Some of the reasons I like to do my own declination correction... No sighting compass can be adjusted for declination. I like using a sighting compass. There is no need to check my compass to see if it is adjusted correctly. It always gives me a magnetic bearing. A mis-adjusted compass give a bearing related to some random number. Hard to go back and correct any past data if you don't know what the mis adjustment was. This is a bigger problem with the Brunton compasses where the adjustment is a friction fit. Once the compass has seen some wear, there tend to adjust on their own. Because I think about declination every time I move a bearing between my compass and my map, I am more likely to have thought about what the current declination is for my current location and I'm more likely to remember what declination is and how it works. I run across way too many people that have either forgotten how and why they adjusted their compass, or worse they had someone else do it for them. They don't understand declination. Sometimes that can't tell me if their compass bearing is relative to magnetic, true or grid north. The often have an incorrect declination setting for their current location. The down side of my choice is that I have to think and do some simple addition or subtraction every time I move a bearing between map and compass. I have talked with some extreme adventure racers that feel they are operating so close to the edge of physical and mental exhaustion, that they have no business doing any thinking and want their compass to do the correction for them.