I don’t know how good a Bluetooth speaker that’s under €30 can really be, but there are a couple of things in this particular speaker’s favour. First of all, it’s really portable, since it’s mimicking a cassette. Back in the old days, you could carry around a couple with your Walkman. Secondly, it’s guaranteed entertainment.
Confuse your colleagues by brandishing a cassette and telling them it’s retro (it worked for vinyl and - apparently - there are still some people clinging to cassettes). Confuse anyone under the age of 25, who have only seen cassettes in those memes that show one alongside a pencil, bemoaning the fact that they will never know the relationship between the two. Or just charge it up and get eight hours of music out of it. Whatever you prefer.