I'm not familiar with the series. But after skimming a few articles on it, I don't think my distaste for Manna transfers.
The Culture series seems to create a platonic ideal of a post-scarcity pseudo-anarchistic liberal society under technocratic governance, and explores its interactions with the outside world.
Though the details of that society's implementation may be somewhat distasteful to me personally, it seems the author is more than willing to critique the society and its behavior from as good a faith a position as he took to create it.
Manna doesn't do the same.
SPOILERS FOR MANNA AHEAD
Brain constructed the Australia Project as a desirable alternative to the corporatist dystopia of the United States - where the majority of the population has been rendered technologically obsolete, and are held in cheap public housing where they wait to die. Despite what he may claim, he writes the Australia Project less as an exploration, and more as a sales brochure.
Brain breathlessly and uncritically describes the Australia Project as heaven on earth, or a 'luxury cruise'. In the process of doing so, he leaves little nuggets of text that suggest a much grimmer reality than he lets on at surface level.
Luxury Cruise is an apt description. You may be there to relax, but the experience is purposeless without the contrast of your real life. The ship may be stocked to the gills, but when things go belly up it quickly becomes clear how constrained the ship's resources truly are. You may be free to have fun now, but upset the wrong person on staff or become even a minor nuisance, and you'll soon learn how autocratically the ship is actually ran.
It's made quite clear that Australia cannot truly be considered a post-scarcity society. In AP, no individual's activities may exceed their allotment of resources (and certainly, there must be an allotment because one's resource consumption cannot come at the expense of another's)
In AP, anyone may be free to create, make, or do whatever they want, but whatever they want is tightly constrained.
No individual's activities may make anyone uncomfortable. This is reflected in Brain's description of the criminal justice system, where he describes automated 'referees' detaining or potentially pre-empting citizen's control over their own bodies in response to an emotional outburst in public, "mainly because no one wants to be around when it happens". He describes this as if it were desirable. If this is seen as a proportional response, I would be terrified for anyone who sought to do or say anything of real consequence.
Finally, as evinced by my previous two examples: everything in Brain's world is on lease, down to your body. Once you're inside of the AP's network every sensation, sight, smell and action is recorded, analyzed, and mediated through it.
Your permission to use your body may be revoked at the leisure of an algorithm perfectly enforcing complex rules of indeterminate (if ostensibly democratic) origin. This happens so often it seems, that it's regard as "sort of like a lifeguard yelling at you at the pool for something you thought was OK".
Your privacy is forfeit, and it's quite clear that the closes thing one can come to owning anything in the AP is inside a virtual space.
Somehow Brain treats this as an ideal future. If this is the best we can hope for, I would sooner be drafted into WWIII than experience it.