My current daily drivers are a pair of Vivobarefoot Ra II. They’re very unassuming and most people don’t notice them, regardless of setting. I’ve worn them everywhere from running to weightlifting to hiking to formal occasions. I’ve worn them just about every day for the past year and a half, the only signs of wear (besides the increased wrinkles in the leather) are some tiny cracks showing up on the toe. The downside is they’re leather, so they require more maintenance than say a pair of Allbirds (another close contender for the ultimate One Shoe, IMHO) and they’re also not as breathable as I would like. Another downside of leather is when I clean them up they tend have a bit of a shine, which is not a look I like in wrinkly leather.
I will say when it comes to running, I don’t like running on concrete in these. I think Vivobarefoot has the right idea about ergonomics (our shoes should be shaped to our feet, not the other way around), but the human body has spent the vast majority of its time on softer ground. Once these give out, I plan on replacing these with another pair from Vivobarefoot, but probably one of their synthetic/breathable shoes.
I’ve also tried the Altama OTB, and ended up not liking them. I found them to be uncomfortable, but more importantly they have a “look” about them that makes them hard to blend in in certain settings. The Allbirds and the Ra’s are extremely neutral and do not stand out, which I’ve found to be important when it comes to being considered for the One Shoe.
If you can go a bit more casual than strictly shoes, I've been loving my Altama's, since doing research on low profile sneakers that will last a long time. Highly recommended. https://smile.amazon.com/gp/product/B074PVP5DS/