many cheap bluetooth audio streaming devices make use of the SBC codec, which is of very low quality.
mp3 and aac are not mandatory for audio streams over bluetooth, so only selected devices support these.
i can't imagine that teenage engineering would go with something like SBC for their speaker, since they have a certain pricetag - which comes with certain expectations.
however, i don't like the design very much, to be honest. maybe i just dislike to place a 30x30x30cm cube in my living room. i'm not a big fan of minimalist interieur anyway ;-)