Xiaomi portable speaker arrived. Took a while, I think because of the battery inside making it essentially powerbank sized.

In terms of build quality it's what you'd expect from xiaomi, meaning it's really good. IP67 rating, 1000 mAh, looks and feels sturdy, relatively light (for a 1Ah battery).
It's a bit thick to just put in your pants pocket (~3 phones thick), but if needed it can fit in there. Perfect for a jacket pocket though.
Connectivity is good, no complaints there.

The biggest importance, and the thing where it really shines is the sound though.
I'm not an audiophile, so I won't know if something is perfect, but I can tell if something is shit, and this is anything but.
Audio is clear, for the size it has a surprising bit of bass, though obviously if that's your main concern you should get something bigger.
The biggest selling point though, is that it gets really loud for the size without starting to sound super bad. It's more than enough for chilling somewhere with friends, even outside, but it's also loud enough that you could reasonably use it as a single audio source for an entire apartment if you have nothing better around. At max volume I can place it in my kitchen (other room, with a hallway inbetween) and through 2 doors it's still loud enough.
In short it's more than loud enough for anything I can reasonably think of ever needing.
The IP67 rating means it's dustproof (highest rating the IP standard supports) and waterproof up to a depth of 1m, meaning you can take it with you to the beach or in the forest and don't have to worry babying it.
Given that I paid 16€ and it's got better audio quality than bluetooth speakers I've seen for 60€, I'm very happy.