I use them because it's the best I can do, but I'm very suspicious. I would think the NSA is misappropriating my tax dollars if they hadn't compromised all of the VPN providers years ago. We also know the US has a history of selling compromised security equipment (https://www.washingtonpost.com/graphics/2020/world/national-...)
Don't get me wrong, I wish the NSA wasn't what it is, but if I'm paying for the federal government to be doing work, I expect them to do it exceedingly well.
So what's the case the United States is so incompetent as to let Mullvad go untapped?
Edit: the answer is that there apparently is no case. maqp was writing up the answer to my question in a response to another comment while I was writing mine.
Edit 2: My personal threat model largely accepts that the NSA, CIA, and FBI can have their way with me in the unlikely event that they notice my existence. I can live with that because they have no reason to take notice. Despite my annoying moral values, I'm not a threat to the state. However, I find the focus on nation-state actors in an ad for a service that clearly can't protect from them to be distressingly dishonest.