Muji is shit, but it's human nature to stick with what you know.
This is a good tactic with tanks - I've spent fortunes on the next best thing only to find they're no better than what I had, but this doesn't apply to cotton.
You can get away with Muji in RDAs or MTL tanks, but you need to be very highly skilled to run, say, a Kylin at 100 watts with Muji using 80vg juice.
Even then, the flavour is nowhere near something like Shake And Vape.
With what most of us spend on vaping, cost shouldn't be a consideration either. Nobody would get through more than £10 worth of the most expensive cotton in a year.