I would give this Grammar 5 stars, but for the following two points.
1) I own the Smyth Greek Grammar and know how truly exceptional a grammar can be.
2) I own the Smyth Greek Grammar and know how truly exceptional an index in a grammar can be.
Those points aside, this is probably the most comprehensive Latin grammar you will find on the market. There are other smaller grammars aimed at beginners and intermediates - Kennedy's - for example, but they don't really come close in terms of breadth of content.
I would not hesitate to buy this if you want the best out there: just be aware that it requires, I think, a thorough going over to get used to the layout and ease of finding what you want in it.