It'd definitely be a nightmare to clean like everyone said
but it'd also be a nightmare for a betta. They'd have to swim all the way to the top chambers with the black caps to get a breath!
Also, I saw a video of this in action once, It's actually a pretty cool seeing fish in there! But I would go insane trying to deal with all the work associated with it.
Imagine trying to get algea off the sides, gravel vacc, and filter the whole thing. OOoh and what if you needed to net a fish or QT someone in there....how would you ever catch them if they can swim into a different section and all the sides are rounded like that!