Search for "stainless steel" and "odor removal" and you'll find a lot of sources to buy objects made of stainless steel that claim to remove the odors that cling, like garlic and onion. You'll find dozens of sources that recommend stainless steel to remove cooking odors and you'll find researchers that insist there's no scientific evidence that stainless steel actually removes odors any better than plain soap and water. Before spending the money on one of these gleaming blocks--or dismissing them as a scam--consider a few facts about the material and its targets.
Stainless steel is a composite material made of steel alloy with chromium. The result is a material that resists rusts and stains, is easy to keep clean and is adaptable for everything from construction materials to kitchen utensils to sculpture. Stainless steel's corrosion resistance is due to "passivation"--a self-restoring layer of chromium oxide that protects the surface of the steel. As the layer wears off, the chromium grabs more oxygen from the air, renewing itself and keeping the steel from oxidizing or rusting. This characteristic means that if the surface is scratched or scrubbed, removing the layer, the process of passivation yields and gathers oxygen to protect the underlying metal. Whether this oxygen exchange or some other quality of chromium ionization is unique enough to interact with and neutralize garlic odor is the unanswered question.
Foods like onion and garlic, both members of the allium genus of plants, contain chemicals that form sulfurous compounds when they react with the air, which means that they grab nitrogen, oxygen or hydrogen. Onion forms sulfur oxides and sulfuric acid when cut. For many years, cutting onions under water and splashing one's eyes with cold water before cutting onions have been ways cooks have avoided tears due to the chemicals formed by onions and air. Garlic forms allyl methyl sulfide, a compound that does not break down in the body but is expelled through pores and breath. It may be possible that flushing these compounds with extra oxygen might help disperse the compounds and therefore the odor.
Instructions that come with the stainless steel eggs and bars direct that they be used under running water. Perhaps some kind of oxygen exchange occurs between the sulfur compounds, water and chromium oxide. Whether the combination of water and stainless steel is more effective than water and, say, coffee grounds, lemon juice, toothpaste or vinegar or some other folk remedy, some inquisitive graduate student will have to discover. At present, no scientific evidence exists to prove that stainless steel works better than more traditional remedies.