I strongly disagree. The real SF element in the book is what if we will not have access to stars? What if we improve our technology to magic like levels but fail to find new frontiers? It is probably the most insightful and most relevant SF book he has ever written. Banks puts the planetary system in isolation but having stars just 4 light years away is no guarantee that we will ever reach them. The premise is species-survival level important.
As for "magical" items, like lazy gun, they serve their purpose best when there are no plausible explanations to their inner workings. They illustrate the point of being made by much advanced technological level characters' better if they make less sense. His choice of extreme cartoonishness, rather than SF classic technobabble is a brilliant invention.
The adventure is great too. A real page turner, if you don't stop to think about implications.