Router bits are generally 2 flute and the cutting edge is not a Helix. Perfectly fie for soft materials like wood. Not so good for metal. They can be used in softer metals like aluminum but are not ideal. Your machining experience will be slow and unpleasant. They can be used if you have nothing else on hand but adjustments to DOC, WOC and feed rates will have to be made and they will all be significantly smaller than a comparable end mill.
End Mills are specifically designed for metals and have very different geometries to router bits for a reason. Plenty of places to get reasonable prices on them from Ebay to some where like Lathe inserts .com are worth having on hand if you will be working in metal occasionally.
Home Depot does carry a product that is very End Mill like and would be the best choice of anything you can get there for working in metal. Still not going to be a good as a proper End Mill but better than a router bit made specifically for wood.
Diablo 1/4 in. x 1 in. Carbide Up Spiral Router Bit-DR75102 - The Home Depot