I have experience of the Boss SP404sx , SP404 mk2 and an older kaossilator .
These are really for home use into a computer imho , or clubbing DJ’s
FWIW, I started off on the Boss SP202 which I still have . Love it for its direct simplicity .
I then purchased SP404sx which is still easy to use and has lots of great effects , plus loads of sample time . Still looking for original 1 gb boss sound card .
I then purchased the SP 404 mk 2 ..and haven’t used it ! Only to update it last April ! It’s too much for me , but is fantastic if you have patience and enjoy menu diving ! Boss give free software updates on the 4/4 annually.
I should really give it ago as it has usbc , works with iPad and pairs with the iPad koala app !
As for the older kaossilator , I won it in a bid on eBay ! No power , and seller soon had it returned ! It looked cheaper , and felt cheap and nasty and left me disappointed . Well it would have done , but luckily I dodged a bullet and got refunded in full . Cheap plastic rubbish