There are a few things to consider when purchasing a reciprocating saw for metal cutting. The first is the size and power of the saw. A large, powerful saw will be able to cut through thicker pieces of metal quickly and easily. However, a smaller, less powerful saw may be more maneuverable and easier to control.
The second thing to consider is the type of blade that you need. There are two main types of blades: those with teeth only on the top edge ( called "top-edge" or "up-cutting" blades), and those with teeth on both the top and bottom edges (called "double-edged" or "bi-metal" blades). Top-edge blades are best for cutting through thinner pieces of metal, while double-edged blades can handle thicker pieces.
Finally, you'll need to decide what kind of features you want in your reciprocating saw. Some common features include variable speed settings, adjustable shoe plates, and orbital action. Variable speed settings allow you to adjust the speed of the blade depending on the thickness of the material you're cutting. Adjustable shoe plates help keep the blade from becoming bogged down in thick materials. And orbital action helps make cuts smoother by moving the blade in an oval pattern rather than just back and forth.