This rule set will be an excellent purchase for some gamers, but not for all.
It contains very clever ideas that build long range projectile weapons into the Song of Blades and Heroes engine beautifully.
However, Flying Lead is a tool kit you might take bits and pieces from, rather than a fully-defined game, and as a result it requires some interpretation. It works very well if one person sets up a scenario and squad lists ahead of time for a friendly, but it would never work competatively, or even in a pick-up game against a 'gamey' opponent. If you want something more clearly developed, other rule sets exist with the same scope.
This flexibility in Flying Lead, conversely, makes it well worth purchasing if you have time to tinker with it. Beyond writing scenarios with these rules alone, you can replace the shooting rules from Drums and Shakos (the nearest equivalent) with those from Flying Lead, allowing you to play American Civil War skirmishes very nicely. Doing the same with Song of Blades and Heroes allows for sci-fi games with guns and alien beasties.
Even when considering it as a tool-kit, though, Flying Lead doesn't feel as finished a product as other titles from Ganesha, as there are several ideas which are casually mentioned but never properly developed. For instance, rules for flamethrowers mention defence provided by "asbestos suit or other material with similar properties", but there are no rules or points values for such suits in the book or the 'builder' webpages (available at the Ganesha website). The 'better weapon' rules for melee combat include a long listing of weapons, but again with no further rules or points values, and in their place a reference to suppliments that never came (bar one). The inclusion of 'improvised weapons' on the list makes the enterprise seem RPG lite rather than wargame. Drums and Shakos uses the same 'better weapon' idea, but presents it less amorphously and with points values provided in its builder. Some of these loose ends could be fixed by fleshing out the Flying Lead builders, but some of it required more attention to detail or restraint of scope in writing of the book.
[3 of 5 Stars!]