Pretty helpful. Well presented, if concise to a fault - no doubt this is the price you pay for breadth of coverage.
That said, you never know whether the point you want to clarify will be in here or not, unless it's part of the core grammar, in which case it will.
But say you want to look up a particular expression to see what MS has to say about how it's used. Couple of examples: (1) 'in particular': appears in two entries, but only as instances, in examples - no discussion, and no contrasting with similar expressions such as 'particularly', which is what I was interested in; (2) 'as to': as far as I can tell from the index, nothing at all on this.
Still, will be very useful for non-native students of English at all levels beyond beginner, and I believe that is the core target market; and always worth searching in for editors and others, which is my category I suppose. Kudos to Swan.