The secret to a successful foot-smoothing episode is not just about the tool.
Sure you want something easy to use, a buffing whatsit with a scrubby and an easy-hold handle. The Tweezerman Pedro Callus Stone foot file ($26 CAN/$20 US) delivers with a handle plus a heavy-duty pumice side for putting the sanding moves on tough calluses, and a finer-grade side for sloughing off dry patches. But unless you know the secret, you'll wonder why your buffing tool isn't getting the job done as efficiently as it should.
The secret is this: use your foot file on clean, damp skin, not wet. Pat some of the moisture from one heel after your shower, then give it a scrubby-scrub. You'll see.
Howzat for simple?
UPDATE: The Tweezerman Sole Smoother Antibacterial Callus Stone ($27 CAD and $20 USD at sephora.com) has replaced this one.