Keep in mind that having a backup image on a external drive is one thing, but being able to access it from a system that has no OS is another thing entirely. Many systems cannot read external drives at the BIOS level, and some imaging software cannot access them from their recovery disc.
An internal drive does not have this limitation, and can serve the same function. If you want to impress your boss with your knowledge and concern for the business, tell him that NO single backup system is adequate, and you need a layered system.
I’d use an internal drive for images of the main drive, with copies on an external drive and additional copies on DVD stored off-site. In the event of a drive failure or Windows melt-down, the internal drive will have you up and running in just minutes. Keep the external drive unplugged except when in use, and it is safe from OS troubles.
Acronis has a scheduling function that can over-write or incrementally create images as often as you wish, and further has the ability to separately back up applications and files. It’s a fine program, but is not immune from the user’s lack of planning for disaster.