If you're happy to vacuum weekly and are already, don't buy one (seriously), but if like me you don't recall the last time you manually vacuumed then buy a $300 Xiaomi Mi and let it do your chore for you.
Plus I've found that they get into places which people ignore (e.g. under the bed, bottom of the closet) and dust still acculates in those places.
It isn't superior to the Roomba 900 series or Neato. It is just "Good Enough" and less than 1/2 the price. Ultimately it doesn't need to be better than the competition when it is cheaper than them, it just needs to basically perform its function.
It may not have amazing suction or intelligence (though I hear newer ones are smarter...), but it will randomly cross over the same spot a few dozen times during its run, and that seems to make up for it.
For me, this means that my environment can be cleaned daily while I exercise or brush my teeth. Manual, time consuming, but admittedly more effective cleaning can now be done far less frequently.
Same with a Roomba - I basically just quickly check a room to see if there's anything lying on the ground, throw it in there and come back in a hour. Clean and in meantime I can actually do my work or something more fun.
Can someone explain to me the draw?