Twins are vehicles from separate brands that share platforms, engines and major components. Product is shared to keep design and manufacturing costs down, with the goal of increasing profits for each of the companies. 
Some twins are sold through a different brand within the same manufacturer (Ford & Mercury); others are available through a competitor (Pontiac Vibe & Toyota Matrix). Usually the vehicles’ interior and exterior styling designs differ, while the engine and suspension are nearly the same.
One brand of the twins may include a lot of bells and whistles at a higher price. The other may provide a more expansive option list for the buyer to choose items individually. One may have a longer running, more comprehensive warranty, and may appear to bring a higher resale value with less initial depreciation. The other twin may be able to save you a lot of money now. Generous incentives may apply to one, and not the other. A personal consideration, you may find that you like one twin’s dealer better than the other. These are all factors to consider. At stake, deciding which twin to buy could save you thousands of dollars.
Manufacturers have shared their designs and hardware for years producing twins. Mercury is Ford, but has traditionally included more standard options. A little more flash, for more money. For years, the Ford Thunderbird was 
essentially the Mercury Cougar. Now, the buyer can choose between the Ford Explorer ($26,495) & Mercury Mountaineer ($26,800), the Ford Escape ($19,140) & Mercury Mariner ($21,540), and the Ford Fusion ($18,135) & Mercury Milan ($19,095)*. Each of them twins. The separate product lines allow for an expanded dealer network, and more profits for the parent company. The downside is in this difficult economy, dealers are competing with each other. For you as the buyer, it gives you more choices, and bargaining power.
The many brands of General Motors have always shared amongst twins, producing essentially the same vehicles under different brands for many different prices. GMC has traditionally been the rougher version of the more domesticated Chevy truck. 
Buick is perceived as the luxury sibling of Chevrolet, while
Chrysler is considered the luxury, more expensive brand, while Dodge is the performance choice, and depending on options, generally costs less. The Chrysler Town & Country minivan ($23,415) is a plusher version of the Dodge Grand Caravan ($22,520). Compare Dodge Avenger ($19,640) & the Chrysler Sebring ($19,840), along with the Dodge
The foreign manufacturers also provide the buyer twin choices, sometimes at considerable dollar savings. Look at the difference between the Honda Pilot ($27,595) & the Acura MDX ($40,195), along with the 
Nissan 350Z ($28,510) & Infiniti G37 ($34,900). Is the name plate worth the extra dollars? The power of twins even crosses between domestic and foreign lines with the Pontiac Vibe ($16,855) & Toyota Matrix ($15,510); and the Ford Fusion ($18,135) & Mazda 6 ($19,140).
While it is generally true that you get what you pay for, with a little research and soul searching, you may find that you do not need all of those options, as well as paying a premium for just a name. Do you really need a Lexus to impress, or is a Toyota Camry with similar options going to satisfy you? With a little humility and common sense, you could save thousands on the purchase price, not to mention the excise tax and insurance. Those dollars saved can buy a lot of gas. Do your research, and ask yourself honestly, "What do you really need?" Then, use the POWER OF TWINS for a smart purchase.
*All prices listed are for Base 2008 models.
