When the construction difference is visible
Most sleeping bags look similar. The WM Ultralite looks different. The baffles are sewn with an even precision that's hard to describe but obvious when you put it next to a mass-market bag. The down fills each baffle consistently — no cold spots, no areas where the fill has shifted. The YKK zipper runs smooth and the anti-snag baffle behind it is properly stitched rather than just tacked. These are small details that add up to a bag that feels like it was made by someone who cares about it.
On a cold night
The 20°F rating performs honestly. The anatomical hood seals well around the face and the draft tube behind the zipper does its job. There's nothing to complain about thermally.